can you believe it? another torsion bar question?? 1.03" vs 1.08"

I think with an early A you can probably get 245's on there with the right backspacing. Although compound is more important, I'd rather run nice 200 treadwear AA A tires in 225 than 360 A B's in 245. But I don't think you'll be getting 275's on a '64, could be wrong early A's are not my specialty.

Anyway, I run 1.12's on my '74 Duster on the street. I'm actually planning on upgrading to 1.14's here pretty soon. The wheel rates depend on who is calculating them, my Firm Feel 1.12's are advertised at 300 lb/in and the MP 1.14's are advertised at 350 lb/in. Of course, the MP 1.09's are advertised at 300 lb/in and SwayAway has slightly different values as well. I kinda doubt the spring constants of the steel are all that different, so it may be in their calculation which makes it a little tricky to compare bars from different manufacturers.

My Duster is no doubt heavier than your '64 and I run 275/35/18's up front and 295/40/18's out back, they're also Falken Azeni RT615's so they're 200 A A rated. I also run Hellwig sway bars front and rear with Hotchkis Fox shocks. I maintain about 1" between my LCA and bumpstop for travel, and even with the 300 lb/in bars I'm still using all of that travel, which is the big thing. If you go too stiff you won't keep your wheels on the ground through bumps, which results in losing traction. But I'm still using all my travel, so, on my car I know I can still go with a higher wheel rate.

If track work is in the future I don't think I'd go smaller than 1.08", even with the car being lighter than mine. I think you'd be in the right ballpark with 1.08-1.14" bars if the plan is to run a high performance but still streetable tire.

For tire size on the early A's, look for some posts by @vntned. You can probably just search "245's" from his username. I know he was running 245's on his early A but I forget the specifics.