For my 1st PowerGlide, I just welded some angle iron that bolts to my steel bench.
jI do some work with the pan side up just laying on the bench. Then for final assembly, put it vertical.

Final_assembly-post.jpg

1993 Daytona, 5.50 at 130mph (1/8) 1.19 sixty ft (PG). Link to 572 B1 - Part 1