I upgraded the suspension and steering systems on my 67 300 vert about 8 years ago. I went with Just Suspension and Firm Feel for my parts.
Torsion bars 1.16" dia
Front sway 1 1/8"
new strut rods and bushings
Tubular upper control arms
Firm Feels level 2 steering box
Rear leaf springs form Springs and Things
rear anti sway bar from FF
subframe connectors
Bilstein shocks all round.
I'm running 15x7 wheels and 235/70 15 tires.
I wouldn't call the ride stiff, I'd call it firm. In my opinion it rides much better than stock! A nice level well controlled ride, everyone likes the ride. Handling is much improved but NOT a sports car by any means...too much mass.