High horsepower and suspension/handling

Hey all- hoping for an answer here since my other forums haven't panned out.

I have a 73 Nova with a 350 that's reaching the end of it's life. The car is my daily so I'm looking into engine swap options/efi/etc etc etc. My buddy has a brand new engine (well, a shelf of brand new parts of an engine yet to be assembled) in his garage, we are thinking of swapping in. The engine is a 383 LT1 w/individual port injection EFI, and an 11:1 compression ratio, that he thinks will be putting 400 HP to the wheels. I am not 100% this is a completely accurate guess ran through a 4l60E, but I'm not a drivetrain expert by any means. He could be right; he's a smart dude. He also has ALL the accessories for the engine, so I can finally have AC

Now; that's a LOT of HP for a daily driver that's already a light car. I want to/am wondering if I NEED to do some handling/braking upgrades. He thinks with a couple tweaks (Need a new power steering rag joint, maybe disc brake conversion) I'd be ok. I'm wondering if I need to go all out-balls out and drop a 4 link in the back; which I'm paranoid about doing because we had some trouble installing my new leafs.

Currently the suspension I'm running is as such- I've rebuilt pretty much all of it at this point.

Rear; New Belltech musclecar leaf springs-stock height Cheapo 25 dollar OEM spec shocks Rear drums-Stock?

Front; New Belltech lowering coil springs-1 inch drop New Classic Performance Parts Upper and Lower tubular control arms; Full new steering linkage except the drag link, power steering box, rag joint, and column. (All new tie rod ends, pittman arm, idler arm etc from proforged) OEM spec shocks (I seriously can't remember the brand on these; got them from o'reillys ages ago)

Should I/do I need to change most of this for a buffer engine? Or could I just throw on some performance shocks. new rag joint, disc brakes in the rear, and throw on some good traction bars? Or do I need to go nuts and do a 4 link kit, coilovers, and all that jazz? This is the first time I've really been doing high performance anything to a car, so I want to be safe/not break anything/hurdle myself out the window.