Years ago when I ran a drag raced a 18 spline four speed I re-fabricated all of the parts.

The trick is to use a factory Z bar as a template, but re-enforce it so that there is 0 flex. I also re-built the pivot ball because it also showed some movement. I also welded a gusset to the mount on the bell housing.

I also used heavier clutch rods until I had it correct. Worked very well when i was done.

I used a Ram, Borg & Beck/ Long style clutch assembly after much trial and error. Contact them for what is the current best system. I know that spring pressures are quite low today and they are very reliable.

If you are going to drag race the thing, do it right and you will be happy.