My friend has a 65 or 66 Mustang, and we need to know where to find the numbers on the block and body to make sure it is "numbers matching" I know the 71? and newer have part of the vin stamped to the block...

 

Near the starter. You may have to pull the oil pan to get some of it.

Here's the google search I did to pull it up... maybe it'll help you more for others numbers?
http://www.google.com/search?hl=en&q...66&btnG=Search

 

Pull the starter to get the casting number for the block. Pull the valve covers to get the casting numbers for the heads. Numbers matching usually means the door plate and the vin stamped on the various body parts match. The casting numbers will get you close but they will not prove it is the original engine.