Clutch questions

[YukonXL04]

Hey Guys, So I have a 1950 Chevy 3100. Sometime in the early 90s it was rebuilt. That includes a 1954 235 from a car. Finally got it road worthy but Im having some clutch issues. It has the 3 on the tree manual and torque tube rear end.

When we first took it out the first couple of miles it shifted great. Then the clutch started slipping, at low RPM's it would grab okay but anything over 1200 or so it would just slip. So I tried adjusting the clutch linkage but that didnt do anything good. So Im wondering before I spring for a new clutch if there is something else I can look into?

It holds good for 1st gear and reverse but not for 2nd or 3rd. The clutch releases great, but when you let off the clutch to re engage it grabs a little but not all the way. Wondering if there isn't a pressure plate issue. Im not smelling burning clutch though

Also if I do have to spring for a new clutch any tell tale signs to figure out which diameter clutch you have before removing the whole transmission?

Its a 1954 235 from a car, the trans best I can tell is the one that came with the truck. It was awesome driving this thing for the first time but it was a bummer cause I couldnt get over about 20 mph lol

Thanks alot!