Need help on engine rebuild on my daily rider.

[Motorbreath22]

Hey guys, I have a late 78' motor I believe sitting in an 82' frame. It is set up as kick only and had the ignition unit from the 82 on it. The transmission has been popping out of 2nd and into neutral and is slipping in every gear in higher rpms. Its leaking oil like crazy now. It has been my daily rider for over a year now and I can't put off taking the motor out. I wanted to rebuild it once I had another bike running but thats not gonna happen so it's getting done now. So what I am wanting to know is where to get good quality transmission parts like pinion gears and shift fork and what not (didn't see this stuff on Mikes XS). I want to have parts lined up so I can get this thing back together as quick as I can.

I am looking into the overdrive 5th gear, barnett clutch, gasket kit and up for some other ideas for upgrades or common parts that wear out that I might as well just order to have ready to go.

Thanks in advance!