Rear Suspension questions/Ladder Bar

[terraplane36]

Hi, I am setting up my 36 Terraplane Coupe gasser style. This is my first attempt, and I am on the junk yard parts budget. I have a 73 Bronco 9 inch going in with welded on ladder bars. If I could afford it, I would use coil over Q1's but am probably not going to get any this year. I have 2 sets of coil springs laying around but don't know how much spring I need. I have an original set of early 60's Pontiac Cat rear coil springs that are probably pretty soft by now, and and a little set of front Corvair coil springs. Will the Corvair springs hold up the rear of a 3000 lb car or will they just bottom out? They look bigger than coil over springs.
How were the 60's gassers set up? I can see from photos they had ladder bars, but can't see if they used coil or leaf springs. I don't think they had coil overs then.