Dex III Fluid. Pick your pleasure. Honestly thats all that matters. There will be the Amsoil preachers and the Transynd preachers and the $20 per gallon preachers.
You will want to build yourself a couple of tools. One would be a bench stand. This is simply a heavy plate that bolts to the 6 bolt PTO flange on the side of the trans. If you have an engine stand, get yourself a pipe that slides into it and then weld that pipe to the plate you made earlier. Drill two sets of holes in that pipe so you can rotate the trans in 90* increments. If you dont have an engine stand but have a very sturdy bench that is bolted to the ground you can just get two pieces of pipe tjat slide into each other, weld one end to the PTo flange plate then weld the other pipe to a plate that you wan bolt to your table.
Another piece you will want to build is a compressor for the C1 spring cage. Take some scrap 4" exhaust pipe and cut a slit in it, this will be the acess point for your snap ring pliers. (O ya, buy a good pair of transmission snap ring pliers)Then put a plate across the top of this pipe and then you can use a shop press, a vice, heck even a drill press to push down on the pipe to compress the spring cage. I chose to build an entire apparatus dedicated to performing this task.
You may need to build a tool to hold the Main shaft in place as well. To do this simple get a piece of scrap and drill two holes in it so it will bolt across the bellhosing. Then drill another hold in the middle and weld a nut on it. Then thread some ready rod through the nut and once you have your main shaft set grab another nut to jamb the rod into place.
Keep lots of trans assembly gel (or vaseline), lots of shop rags and lots of rubber gloves handy. Just keep everything clean and take your time it will go fine.
Heres pics of my tools i built.