I'm looking for a new stall converter. I'm having issues with shifting to drive or reverse there's a pretty hard jerk with about 1200 rpm idle (cold with choke on, although it shifts all gears with a nice firm shift) plus I'm wanting the performance off the line as well.

1972 C10 1/2 ton
mild 350, performer rpm cam (soon to be 383 with larger duration cam)
700R4
3.73 rear gears
~ 28" tires.

1) I was thinking either a 2400 to 3000?
2) Also how do I know which spline I need? I've seen 30 and 27.
3) Also advantages disadvantages of lockup?
4) Brands good bad??

THANKS!