He has to install some new part on his 1981 F-150 Custom, and first off we need to find out for sure whether the thing has a 351M or a 351C. Naturally you would think that it has a 351M because it's a 1981 and the 351C was retired in 1974. BUT.... before he bought it, it had a new or rebuilt motor installed. So I am wondering maybe if the previous owner installed a 351C instead because of the poor rep of the 351M. So... I don't know how to tell the difference by looking at the motors, they both look the same. Maybe you can't tell the difference without looking at casting numbers, I dunno. Anybody know how to tell the difference?? Secondly, he wants to put on an aftermarket intake manifold and carb. If it is a 351M, will an aftermarket intake and carb for a 351C work or does it have to be specifically for a 351M (if there is such a thing)? Any help would be awesome!