The most important thing to remember about installing the main drive gear race into the tranny case is that what ever tool you make must press the bearing in by the OUTER race only. You don`t want to cross load the bearing.
When you install the main drive gear into that bearing, you want your puller to immobilize against the INNER race as it pulls the drive gear into the bearing.
I bought the tools from George`s garage, but you could pull the bearing/gear stuff in with a tool made up of long bolt/pipe or sockets, just make sure you don`t cross load the bearings.
Removal tools cross load the bearing during the removal process, that is why they are tossed into the scrap pile and not re-used.
I remove the jackshaft seal by driving it out with a drift. Install the new one using a puller made up from a couple of sockets/bolt/nut.
The big oil seal, I just pry it out with a screwdriver. Install with a mallet and a block of wood.
The quad seal slides over the main drive gear, no tool needed.
I use the tool from George`s garage to install the small oil seal that goes in the main drive gear. It also will install the needle bearings into the main drive gear to the correct depth.
If you are replacing the main drive gear oil seal while the mainshaft is installed, you could fabricate a tool with pvc tube, but don`t wack it too hard, you don`t want to damage the ball bearing.
Hope some of this makes sense…