hello first timer

Welcome to the board.
I did run on the street with the 6cly torsion bars, with a big block under the hood.
Handleing was horrible at best. The brakes worked, but I did have the rears already upgraded to the 11" drums. But I evntually switched it to disks up front.
You need to be able to stop these things.
I'm not sure about the weight difference between the /6 and the small block, but the big block was a bunch heavier.
You might want to do a good inspection of the front end parts before you get the new engine in. I found a horribly bad lower ball joint, at that time
Good luck and keep us updated on the progress.