A BB in a old Chevy 2 is a lot of work. I had an LS6 in a 66 nova. You have to cut the fender wells out to clear the exhaust, then you have to reinforce what you cut out to keep the car from falling apart. The stock front springs won't work, the BB is much heavier. I had the some big slicks on the back and it twisted the body so bad it was hard to shut the doors. I ended up with frame connectors and a cage to stiffen the car.
Go with a small block it bolts right in.