4 spd. pops out of gear.

AJ, I performed a few of those tests you suggested, with the car still up in the air.
I instinctively bump a higher gear with these old trans before I go for first so as not to get a grind, but waiting the 5-10 sec. before shifting none of the gears ground at slower rpms .
On the road at higher rpms the gears will grind. Help is hard to come by so I try to do every thing myself. With the pedal propped to nearly the floor I can slip a .050 shim all around the airspace, the disc spins freely and no wobble, all new stuff except trans.
Any more air space needed I will have to modify my homemade Zbar. .050 seems plenty? but I`m no expert. The trans installed too easy/nice to think of bell misalignment.
BUT the engine was from an auto 440 car, 72 forged crank newyorker, pilot bearing tapped in nice and snug.
I`m working up the gumption to get it drained ,pulled, and opened up for a look see, and try to restore this thing myself. I`ll post a few up closers and with a new kit from Dan, and hopefully a little help from all you guys, I can get r done.