Stick with a 2 bolt main and a 1 piece rear main seal, they don't leak as much. I have been beating up 2 bolt's for many years and not had a problem that was due to the 2 bolt. In fact the engine I just built for my S-10 is a 2 bolt, and I have a 4 bolt on the engine stand. I used the 2 bolt because it has the 1 piece rear main seal and it is a roller cam block. 2 bolts are much easier to find and they hold up well.