Going Powerglide

Hello, I am going to a powerglide in my Dart. It's is getting a JW Bell so It will bolt up nicely, however I am also installing a mid plate (1/4") which requires a crank spacer and the Chevy flex plate which also requires a crank spacer. Has anyone tackled this before, and if so what length flex plate bolts you used or any other pointers you can give me before I begin this swap.
If big block then yes and you'll have to do all the calcs based on the different components you'll use. If you don't have anything yet let me know because I just built a entirely new PG and I'm not using most the old pieces. It was built for around 800HP and I'm trying to make over 1000 now.