My experience with OEM starters has been that the early 3-bolt starters are the same as FE, the early (high mount) 2-bolt starters are unique to the straight sixes, and the later (low mount 200 & 250) 2 bolt starters are the same as small block Ford.
Both type of 2 bolt starters actually have the same bolt pattern, but the early starter nose puts the plunger and power stud in the right place so it doesn't hit the block in a high mount configuration. That said, some universal aftermarket starters allow you to align the body of the starter how you want, so that design of starter would probably interchange between the high mounted six and SBF as well.