Actually it's 170, 198, and 225. The 198 and 225 use the same block, which is a bit bigger then the 170. All engines use the 3.40" bore and the cranks all have different strokes. The heads are all basically the same and most parts interchange easily except cranks and some valve stuff. Later engines used hydralic lifters. All engines used forged cranks until around '73~'74 or around then, when they went to cast.