Ok guys & gals, here is my story and I wish to stick to it.
1971 FB with original FMX, swapped in a toploader from a 73Q car and now a Tremec TKX.
For the TKX, I went with the 10 spline unit and re-used my 11'' long clutch.
Now I am wanting to go with a diaphram clutch, and that is easy enough...