I'm missing something. You identified the open driveline transmission as what you have and then state that you have a closed driveshaft. They are completely different.
Why not find a used stock torque tube transmission, install it and go on down the road. They are advertised on this site all the time and are relatively inexpensive. Many are removed for upgrades and are perfectly useable for stock applications. Why make a bunch of modifications when they are not needed?
Fred



1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine