Just wondering if anybody knows of an off the shelf exhaust kit that will fit a 68-70 Javelin from the headers back.
 
Maybe something for another car that will fit on with minimal mods.
 
Looking for a twin 2 1/2" system with an X-pipe and mandrel bends. Car is running Hooker competition headers.

I used the Mustang tail pipes on my 73 Javelin and I used the x pipe designed for early Gm F body from Pypes here in the States.  
Had to do some cutting but it wasn't too difficult. I used a large tubing cutter to cut the pipes, it left a nice clean edge with out a lot of sharp burrs.  
 
http://pypesexhaust.com/
 
XVA10  XVA10S    2˝" X-pipe Kit   (W = 21")  
XVA13  XVA13S    3" X-pipe Kit   (W = 21") Diagram  
XVA14  N/A    3.5" X-pipe Kit - NOW IN STOCK  
 
 
 Special X-pipe. Allows exhaust pipes to mount in the driveshaft tunnel for better clearance. Modification of body pan is required on convertibles but can be done!  
 
NOTE:   1967-69 F-body Convertible owners cars were originally equipped with a body pan reinforcement brace located directly under the transmission tailshaft. In order to utilize our X-pipe, it is necessary to either add RPE631FA spacers that lower the body pan to allow clearance for the X assembly OR remove the body pan and install subframe connectors.  
 

I tried the Mustang LX pipes on my old '70 AMX and it wasn't even close. Right now I'm in the middle of exhaust on my '69 AMX using '70 Chevelle tailpipes. The only thing usable is the tubing going over the rear axle. Everything else has to be pieced together. I got an 'X' pipe kit from Jegs that works pretty good. All I need now is two 'J' bends for the tubes going out under the rear bumper. I'll post pics of the finished pipe when it's done. You're Javelin tailpipes should be the same.
 
-Steve-
 

 

 

 

 

 

That looks pretty good Rebel Machine.

Any suggestions on how much overlap the x-pipe should have?

Yes, will just be fabricating my own X-pipe, cut the outside of a couple of bends off and weld them together. Just thought there might be some rule of thumb as to how big the hole should be or maybe something to do with the combined cross sectional area. Hopefully not too critical.
 
You can probably see from the work so far that the X-pipe will be just under the front uni joint.

For placement, most stuff comming up on google suggests closer to the headers is better, but there are also reccomendations for closer to the back, in the middle or at the hottest point. I think the reality is that with a live rear axle setup like our cars, just behind the transmission is the only practical place to put one.
 
There also seems to be a few variations on the x-pipe design, this one is particularly sexy:
 

 

Well, that's enough shiny stuff, lets get back to my more agricultural efforts: