Monza rotors, vented after '76, fit...I had a '74 Vega with a 215 aluminum Olds motor with G-body front brakes and spindles, adapted with a little a-arm fab work, which along with the G-body aluminum rear drums hugely upped the braking power as well as improving the camber curve. Rear suspension needs nothing to be good for handling, except both ends need stiff swaybars and shocks. That car and other Vegas I had including with a built-four handled very well, it was a good suspension design for its' time. However even with the very light engine, after a couple years the front structure was coming apart. A bunch of sheet metal stampings spot-welded together, which bent, cracked, and peeled apart...the guy with the car in the above link is going to find all that out. With that unfortunate weakness, stock Vega suspension IMO is actually better than the stock mid-year Vette suspension which has an IRS originally designed for 6" wide bias tires, so there goes much of the sensibility in that swap besides the substantial packaging issues. I used to run my cars up in the So. Cal. canyons pretty hard, always down on power a little compared to most cars, just barely behind the Porches on cornering but ahead of any larger car. Corvette guys would never race so who-knows.
None of this was with small-block cars where the headers hung so low you had to creep over standard driveways. I built one of those too, with a friend, tubbed and all that before everybody was doing it, was good for straight-lines and looking crazy but not much else.
When Vegas were a dime-a-dozen and lined up in the scrap yards untouched was the time to be trying all this stuff, I wouldn't do it now unless I happened to have a couple around already. My last Vega, after half-a-dozen built ones, was a dead-stock "Millionth-edition" '73 that I wish I'd kept.