How can I verify the engine that is in my car is the one it came from the factory with?
I have bought 2 1966 Mustangs recently. One has a 2 bbl carb and the other has a 4 bbl carb. Is the 4 bbl carb motor the hipo engine or the 225 hp and is there a difference/
There really isn't a definitive way. You could check the date code on the block, just above the starter. If that date is prior to the scheduled build date of your car then more than likely it is original but that isn't certain either.
Unlike Chevys and Shelbys, regular Mustangs didn't have the cars VIN stamped on the blocks. That date code is as close as you'll get unless you bought it from the original owner and they can verify.