Odd shifter problem, need advice

Dan, Power shifting was never the problem for me with either. I found the 6 " always shifted into reverse and other gears easier when the car wasn't moving. But I never tried this with your upgraded synchronizers

What I did see was when the diaphragm style pressure plate is used with the over center spring in place and you pull a gear while holding the throttle flat to the floor. " Flat Shifting" The pressure plate will not re-engage until you let off the throttle and the RPM's come down. Just ran into this with the Barracuda for Todd I built that trans for that needed the second gear that was popping out of gear.

I myself only ever had 5 1/4 and 6" pin spread . I never saw any other spreads but that doesn't mean they were never produced.