Best Trans for Swap

26.6s will get you 65~3065@zero-slip with 3.73s
the A500 would bring that down to 2110,still zero-slip.(loc-up).
This gets you a final-drive ratio of; 3.73 x .69~2.57.
The starter-gear would be 3.73x2.74~10.22. It would not take much engine to make this a tire-fryer, in an Early-A. The hard part will be limiting the cam-selection to actually take advantage of the 2110 cruise rpm.
35mph will be about 4750 so it won't take much more than the stock cam to make her a potent stop-lite bruiser.And that is a good thing, cuz the 2110 cruise rpm also wants the stock cam, to be fuel efficient.
At the factory 9.2Scr this would be a fairly nice combo for your stated useage. The only improvement I could imagine, would be slightly bigger .050, solid lifter cam, with similar-to-stock advertised specs, with a tighter LSA, paired with headers; for the One-Gear blasts to 40 mph/5500rpm. Second will get you 72/5500.
Yur gonna need to fix your traction issues first tho.
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FYI
I think I would run that A500 with 4.30s for a 2-gear blast to 60/65 and cruise at 65=2440 in lock-up. This would allow a bit more cam and a bit more cylinder pressure, which would require a bit more tire and a bit more finessing off the line. 4.30s would get you 65=5700rpm in second so a 5400 peak power, so about a 225/230@050 cam. It will like those 4.30s alot. But..... you might as well leave the 2bbl on her cuz you won't hardly get to use the secondaries .... for all the tirespin on the primaries,lol. I ran this combo with a totally stock Lo-compression LA318 long block, with nothing more than headers and a big ThermoQuad,in my 3650 pound 68 Barracuda, and it was a flippinUge blast. But first gear was a bit short lol, with the stock cam. 295/50-15s gave up right away with a 2800TC, even with the SureGrip.I revved that teener to 5500 regularly.
I only ran it that way for a few weeks, cuz that 318 was my winter engine.It usually ran less than 3.23s; as low a 2.73s. And usually studded winter tires once the snow came,usually in December, to March/April. The Barracuda was not a very good winter car, but it's all I had. Mostly it was front-heavy.If the front decided not to roll, I wasn't going anywhere.