Rear End Gears

Your A500 actually has a .69 overdrive not .79
I just recently did the A500 swap. I,m running 3:23 gears and 225/60/15 rear tires, which are around 25-1/2" tall.
Seems to have plenty of low end, with the factory high stall converter that came with the tranny, and the slightly lower first gear, it will smoke that right rear tire no problem.
But I am running a 5.9 magnum.
With this setup the overdrive is great. 60 mph is barely 2000rpm. 75mph is like 2500
I think it's going to be great cause I do a Lot of highway driving.
But,
I'm thinking of switching to 3:55's as well, already have a new set on the shelf.
3:23 to 3:55 is a pretty small change so it shouldn't change my highway rpm much.

I'd think that running a 273, you might want to go ahead with the 3:55's, since you already have them, might get you off the line a little quicker.