Shift improve kit

[JAM1777]

I installed a new rear main seal, new oil pan gasket, new bm holeshot 1900 to 2100 converter and tomorrow im servicing the tranny with a filter kit. I know that if i want to install a shift improve kit that it would be the best time cause the tranny is out. Any suggestions on a good shift improve kit? This will be the first time im going to open a tranny but im pretty mechanically inclined. Do kits come with step by step directions and specs? And can it be done in one day? I wont be racing it but i want to know i have the power and get up there. Its a 350 4 bolt main small block with a turbo 350 tranny. Thanks for any help and advice.

1969 chevy C10 longbed