I've been in the process of similar upgrades to my 66 coupe and can share the following
I'm in Canada so options for suppliers is a bit tough because of shipping cost. I tend to go to Summit for most things as they have good prices and shipping is cheap or free to Canada. It has limited my options a bit
Most of what I've been installing is under the Scott Drake brand. I know the brand isn't what it once was but I haven't had and major issues except for some front springs that sat too low. Everything else has been fine.
You can check out my progress in my build thread if you'd like.
SD power disc brake conversion. Happy with it but in hindsight might have been happier with non power, but I will likely never know.
Cooling upgrades. Stayed basic with a 2 core aluminum rad, 6 blade clutch fan and an OEM shroud. Seems to work well
Suspension upgrades. SD coils and 5 leaf stock height all matched with KYB gas adjust shocks. The front sits too low so I'm fixing that. The rear is higher than stock but I like the old school rake. The shocks a wee bit stiff but I'll good with them and didn't want to spend more.
SD export brace and Monte Carlo bar. Tough install but a must do in my mind.
Wheels and tires. I did 15" TTDs, 7" (3.75 BS) front and 8" (4.5 BS) rear, 215/60 front and 235/60 rear. At first everything rubbed the fenders when hitting bumps, front and rear. With the rear leafs done and the butt up a bit from stock, the rear no longer rub but would at full suspension travel. The fronts have been a challenge and I still don't have it fully solved. One side seems to just clear and one side doesn't quite. I'm hoping that after I'm at stock ride height and have a good alignment with a wee bit of negative camber, my front rubbing will be solved. I can probably pick up a little clearance with a fender alignment tweak as well. I don't want to roll the fenders so if all else fails I'll pick up some 6" wheels for the front. That will definitely move the outboard edge of the 215 inward enough. Fun and games.