You should be able to use the old snap rings, unless you have excessive clearance issues - i.e. popping out of gear. You need a few special tools, a press to disassemble the mainshaft, pullers for the gears on the back side of the intermediate plate (5th) which can be a bitch to put together in the right setup so you don't damage any gears, snap ring pliers, a pin punch (can't remember the size), plastic bags, and a roll of masking tape with a sharpie.
I paid a helluva lot less for my parts, because DM has an overhaul kit. Call them and he will give you the price on the kit. I didn't replace any gears, but I wish I'd had the time/money to replace the reverse gear and idler. I couldn't wait for the reverse gear to come, so I just threw it back together with all new bearings and synchros. Reverse is not exactly important to me lol.