welcome ... What was your Swinger equipped like ? What color ?
I am redoing one as well... R4 red .
your gears will depend one your engine build and driving conditions... if you are going stock engine and drive on freeways/hwy a lot than I would go no higher than 3.55.
I just put 40 hwy miles on my 68 fsstback with 3.55s this morning and anything higher would have been revving to much for my likes.
