Trans issue

[truckeroy]

I just bought my 64 and it had screwed up linkage on a floor shift conversion. It wouldn't hold in 1st because it hit the seat, but i thought it might be more than that. (a lower price point). i put in a new shifter and the trans seems to want to jump out of 1st and I hear some growling. So it looks like a trans change may be in order. My question is what 3spd will fit in place of the original? Was a different trans used after 64? I realize the clutch spline and drive shaft yoke spline is different in some designs, but what will interchange with my 64? A 4 spd would be fine, but the cost goes up, I know. What is the best way to go, short of an auto? I put an s10 in my 40 pu, so I guess that's an option here except for the cost. Thanks, Roy