Front disc’s first. You’ll have plenty to do right there.
I would look into electric power steering, thats what all new cars have, get more room for headers and such.
Why air shocks? That’s so 60’s. You will hate the ride quality.
New re-arched leaf springs is the way I would go if I wanted to if I wanted to stiffen/raise the rear.
There are plenty of disc brake kits out there, someone here will chime in.
Nice looking car by the way.