65 Valiant 904 no reverse.

Hello, my 1965Valiant wagon with a column shift 904 trans that was rebuilt 2y ago with a rebuilt engine then the car sat. 6 months ago I started to finish up the exhaust, cooling, and some electrical stuff, during this time I ran the engine 20 minutes at a time and slipped into all the gears maybe 4 hr. of run time.
? Yesterday I dropped it to the ground all ready to go, and Reverse doesn't move the car, I feel a slight engagement. thank you.