Edit: This is from Treeroot's 465 install.
You will need to modify four things on the SM465. The first is the front bearing retainer. It needs to be turned down to match the bell housing. Bruce Lawson offered to machine the parts for me and I cannot thank him enough for his help. The four bolts have to be replaced with Hex style bolts to clear the bell housing (5/16-18 x 7/8”).
The second is to sleeve the collar for the throw out bearing. A piece of exhaust pipe cut to 7cm has the correct inner and outer diameter (1 3/8” ID & 1 1/2” OD). Part #548530. Welding to cast can be done but I chose to solder the collar to the bearing retainer. Use acid flux solder, make sure everything is clean, and rough up both parts so there is a tooth on both parts for the solder to stick to. Heat will destroy the inner seal so why not just replace it. NAPA part #16054. The gasket between the bearing retainer and transmission is available at the dealer, part #12337932.
The new pilot bearing has a longer inner sleeve to support the input shaft of the SM465. The input shaft is approximately 1/4" shorter. I bought mine from A&W Bearing Supply ,800-535-9638. Part number BCA 202RRE. I pulled the info from a old TLCA BBS thread. If you have the transmission out of the truck, now is a good time to replace the rear main if it is leaking. Instead of the expensive SST, use the cone off the rear of a stock t-case. That and a rubber mallet work perfectly.
For the clutch assembly you can run either the 3-speed with the 3-speed flywheel or the 4-speed with the 4-speed flywheel. I reused the 4-speed throw out bearing, pressure plate, clutch fork, and flywheel. An 11” Chevy clutch disc replaces the stock disc because the splines are different. This was one of the biggest delays in this project because none of the major part stores will sell just the clutch disc. They only sell kits now. After some searching, Dial-A-Clutch came through with the disc. AutoZone is the only place I found that carries the alignment tool.
http://www.root45.com/SM465Orion/