If I owned a Chevy it would mean that the block s/n matched the vin. But what does it mean when associated with AMC?
 
Later!
Mr. Ed

It means nothing other than the vin number on the shock tower and behind the steering box on a 68 should match your title, or that the vin number on the dash of your 69/70 should match the vin number behind the steering box and on your title.  
 
There is no engine or trans numbers that will match your vin number.
 
There are numbers in the block casting that will tell you when an engine was manufactured, but pretty much any same size engine from any AMC vehicle built around the time your car was built would be as correct as any other.

I agree with all of your replies. There is a dealer selling a "numbers matching" AMX on e-bay for big bucks so I asked him what he meant. He replied with a long littany about the block castings and serial number sequences but in the end he admitted that it meant that they "checked out" the car. Sad what some people will do to jack the price up. What's even sadder is when some poor fool believs the numbers matching BS that some out there are using to sell a vehicle, regardless of make.
 
Later!
mr. Ed

Larry is generally correct, but I disagree with Mr Ed's last post. If the car was thoroughly checked and most of the date codes come close to the build date (assuming the build date is known) then it's as close to what collectors mean by "numbers matching" as it can be, and that should justify a higher asking price than one with numbers definitely out of range. A 69 AMX with an original 1969 390 should be worth more than say a similar 69 AMX with a 1970 390 -- even if the 69 engine was pulled as a replacement from an Ambassador but has the date code within a couple weeks of the original 69 build date. If I knew for sure the engine was a replacement from another car I'd probably knock a couple hundred off the appraisal price, but that's it as long as it was a 69 engine. The 70 engine would knock the price down a couple hundred more. Appraisals are rather subjective though. That original engine in an otherwise highly modified car wouldn't mean as much as a non-original engine in an otherwise 100% correct car.  
 
For historically significant or serious collector cars it is important to get the date codes all within a reasonable time frame. The engine date code shouldn't be more than a month prior to the build date, for example, and shouldn't be after the build date. The trick is finding the build date. On pre 69 cars that can be difficult. It can be difficult on ANY AMC unless one is lucky enough to find the build order in the car. For some, such as the AMX and Javelin, there are build date charts showing which final assembly numbers (VIN is unimportant -- that was assigned as cars were ordered, not built) were built in which months, but not for all years. So it's hard, and most of the time impossible, to determine if the engine is truly original to the car. The number tag on the valve cover (generator bracket on Gen-1 V-8s) can be easily swapped to "hide" an incorrect engine, or even restamped. For cars with VINs instead of serial numbers (1966 and later) the engine size and trans type should match the VIN, but that's the only thing on the car to match up. It takes a knowledgeable person to even find that! Only the sixes have the engine number stamped on the block, those can be easier to identify as "most likely original" or not -- but still no way to determine precisely.

Quote from MrEd on 01/20/11 at 18:21:31:

Ed,
 Frank will usually give people the benifit of the doubt, I guess he's just too nice of a guy. A used car dealer could consult with someone who has knowledge of AMC date codes so it could happen, as unlikley as it may seem. I guess you lean towards all used car dealers being scum so you can't believe a thing they say. I can't say for sure where the truth is in this case, but I will agree that "numbers matching" technically does not apply to AMCs.
 
 In the end the old saying "buyer beware" is good advice. "a fool and his money" and "an a** for every seat" seem to apply quite often as well.
 
Dave Z