Like Don and Tech point out, the rear gear ratio is only one piece of the puzzle. With your TH350 ratios of 2.52, 1.52 and 1.0 you are going to be putting a lot of strain on the tranny every time you take off, especially if you push it. If you use 3000rpm as your "predicted" shift point your speed for 1 to 2 is 39mph, 2 to 3 is 64mph and you will cruise at 97mph in third at 3000rpm. I don't think you will be happy with those tall tires and tall gears if you liked the way it performed last year with 25" tires, but like Don said, bolt it up and try it. Changing to 3.08's yields 2415rpm @ 70, 3.42's gives you 2681rpm, and 3.73's takes you to 2924rpm, just about where they ran back in the day - 3000 @ 70 and gulping gas. An OD gear would make things a lot easier to balance.