[Transformula]

Look at the model # of the trans. FS is direct top gear, FSO is overdrive top gear. Here's th breakdown: F=Fuller, S=Synchronized, O=Overdrive. 6= 650 LbFt torque input rating, 4= design level, and 06= forward speeds. It would require a few gear swaps and countershaft swap to make a non-overdrive into an OD. Better to find the one you want to begin with to save money. Yes, there are two different pilot sizes, the small for smaller applications, for what you are doing, and the large one for things like Cat engines, etc. The spline size stays the same. I've never had to measure the bolt pattern, but I know it does use 15/16 headed bolts (5/8 shank). To make a guess, I'd say the upper bolts are about 12 inches apart, as well as the lower, and maybe about 9 inches from top to bottom. If I remember, I might be able to get some measurements at work next week. I wish I knew more about the chevy gasser engines in front of these, and the parts that go with them, But I work on the Big Rigs.