Torque boxes and frame connectors. When are they required?

Well, the title pretty much sums it up. I'm about to drop in my 500 HP (Hopefully) 440 and I hadn't thought about beefing up the frame. When is it required? If I get frame connectors do I still need torque boxes? Who makes a decent set of these. Preferably a bolt in set. I'd also rather not cut the floor.
Also I was running the slant 6 driveshaft with my mild 318. Is it ok to keep using this as long as I get a loop for it? Brewers has the U joints to make it work. I'm just not sure if it will hold up. Any advise is greatly appreciated.