[Harry The Hammer]

I feel for you.
FWIW:I had a 77 Camaro that would stick the shifter like this & had to crawl under the car & move the levers on the trans by hand before it would work again,also had to move the bowl on the steering column.
Check your linkages for play & the trans levers

[Goathead66]

Is the bellhousing concentric with the crank ?- aftermarket bellhousing aren't real exact on their location in re-guards to the crank. When I put my scattershield on- the bore was way off center to the crank and had to get eccentric locating pins (Lakewood). Most clutch manufacturers stress the use of an indicator to make sure the crank and bellhousing bore lines up. There is a gauge available to make it easier as the indicator method is a pain. Just my 2 cents. Good luck