goin from memory, I believe the cc is 1.6 cc per 0.010 milled, so an 0.015 cut would be about 2.4 cc.  If you have a copy of Performance American Style its in there.
I have a similar 360, but with headers, 750 Holley, and a torker intake and based on its 12.0 at 115 mph performance I estimate it to be making about 400 horsepower.  The heads are not ported, but they were prepped by a local race shop which has been shown to help by 30-40 HP on other engines.  So I would estimate that you would be 350-400 HP depending on the exhaust you run, and the valve job on the heads.
ralfy

machining off 0.001 will reduce the volume by 0.16cc
 
Norm

Depends, so you give or take would be right back at stock volume. You could look at valaves with flat bottoms instead of the stockish relieved ones but the cc reduction is probably infinitesimal. With .090's the shrouding with stock valves is minimal anyway. Since stock volume on 58cc heads is roughly 57 to 59 you'd need to mill more off or go with specific pistons to get whatever your goal is.
 Steve

A set of vintage 343 pistons would work too. What are your goals as far as characteristics you are looking for? Acceleration? Top Speed? Responsiveness with broad torque? What kinda car? Jav, AMX, Hornet? Manual trans? Are you seeking handling as in being able to switch from right to left, maybe drift a little with predictable results? Straight line?
 Steve

I had a set of 51cc heads re-done, they were cut to clean them up, and then the valve job was done with larger valves on a machine that also unshrouds the valve and the chambers ended up at 53 cc.  
If you are a noob I will repeat what has been said in other threads, but this is the thought process I recommend
1.  Decide what you are going to do.  Most important decision is how much you are going to drive on the street and what fuel are you going to run.  Assuming you want to be able to run on pump gas, you want to keep the dynamic compression as defined here: http://www.kb-silvolite.com/calc.php?action=comp2  between 8.3 and 8.7 to one.  8.3 is a safe number, 8.7 is marginal, may require octane boost, may require the timing to be pulled back but will work for occasional street use and trips.
2.  Make a realistic assessment of the rpm capability of the engine.  My advice is never ever plan on running cast pistons and rods over 6000 rpm.  This drives the cam selection, more duration means higher rpm to get in the power band.  Pick the cam for rpm, then use the silvolite calculator to guide your compression ratio.  As a general rule, a cam with 220-224 intake duration at 0.050 is a good cast piston choice, power band to 5500 or so.  If you go up a bit in cam, 230-237 intake duration at 0.050 power band will easily go to 6000 rpm and pushes the limit on cast rods or cast or hypereutectic pistons.  Not a grenade motor, but pushing to the limit.  About the most cam I would recommend for a car that really will be driven regularly on the street is an intake duration of 245-255 at 0.050.  That should get you to a power band that peaks at 6500-7000.  Probably the most extreme street vehicle on this forum is Steve Keown's street driven 10 second AMX.  His intake duration is about 261 at 0.050  At this point I had power brake issues, Steve is I believe still using power brakes.  The cam that Ken Parkman used for his engine builder challenge engine was I believe 254 duration at 0.050, a good choice for a competition where overall torque is important not just peak horsepower.
3.  Once you have the cam and compression that meet your powerband objectives, you will need to build the rest of the engine to take that power level.  With cast pistons and 5500 rpm, a pretty much stock rebuild will be fine.  Above 6000 rpm you will need balanced forged internals and good valvetrain.  If you want to push to 7000 rpm, the heads will need to be upgraded to support that power level.  
There are basic things that should be done to any AMC V8, improved oilpan, improved valvetrain, and so on.  Good luck.
ralfy

Building on the advice above, and I'd stick with the more conservative .050 specs, particularly with stock cast pistons that are stock weight. It's not so much the rpm's determine cast vs. forged as it is reciprocating weight ( including rods and piston pins)  for cast vs forged. I'd say that 5500 is a conservative limit for the 360 piston/rod combo vs. a 390 or 401 cast piston/rod combo. But 5500 is a reasonable limit and if you pick the right cam after you pick the pistons, determine deck height and head gasket thickness, plus any head work- like bowl porting or extra cuts to the valve and seat- you can get the meaty part of the powerband below that or you can install and ignition box with rpm limiter to keep max r's inline with piston reliability if the engine wants to pull beyond 5500 or so (  my thought is with a quality set of brand new casts- 5800 would likely do no harm- but haven't tested that personally ).
  Crucial, if autocross is in the future, is looking at this gentleman's experience and seeking his advice:http://www.theamcforum.com/forum/the-story-of-my-engine-by-ray-larson_topic12796 .html . I'd recommend peripheral to that based on a respected vendor's advice- getting a 7 quart pan ( and a crank scraper ) as a minimal start for lower end mods when consistently throwing a car through a series of turns. Bulltear might have both or he has scrapers and possibly redos of the 6 quart police pans. If you ran an extra quart with a police pan and a scraper you'd likely be ok. Ask Kelvinator on here about that.
  Another place to look for at least a fatter front sway bar is an Eagle ( like the sports oriented SX-4 ). The rear attaches much different through a pair of rubber lined clamps. If you got the rear set-up complete too- there's no reason I see that you couldn't use the Eagle rear bar. I'd have to look to jog my memory as to if you'd have to drill the rear frame rails. I seem to recall the clamps attach to what looks like an idler arm bracket and pin that bolts to the frame. Another choice at a reasonable price is a used set of ADDCO bars.  
  Hope these thoughts help.
 
Steve

Honestly, until I get a line on some better income, I probably won't be building the bottom end - so I have time to decide if I want to go all out or not (plus I can always upgrade cams later, the big Summit one is only 59.99)
 
Will the cast pistons work well with say, a 100 shot of nitrous, or should I abondon the idea and just save for when i actually do rebuild the bottom end?