I don't quite get what you mean by main bearings that have been turned. Whe I build a motor I make sure and line bore the block to make sure that all the crank journals are perfectly true. After making sure the crank is right I just install the proper bearings with assembly lube and go for it. As far as the gear drive goes. just make sure and read the directions that came with it and you will be fine. PS they really make a blower stand out