Any thoughts about how lowering the rear pivot point by adding a spacer between the spring and the mount would act differently than going to the top front hole from the bottom? Both ways would make the Caltracs hit quicker. I can vouch that adding a 1" spacer 'tween axles and spring will hit the tyre harder and increase axle rotation. Top hole on front bracket always hits harder so much that it will likely "wad up" a std bias ply. Front travel is also important on how it hits, less front travel will cause porpoising (load and unload of the rear) but this is also dependant upon Hp/Torque and weight. Tubes and Stiff sidewalls will help but my Caltrac setup works great on Radial tyres. This is what has happened on my car, in a nutshell as I've been running Caltracs since 2001. Though your results may vary 
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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