Overdrive trans or change rearend/gears

[BuiltwithIvy]

the best option for all of the above is honestly both, Ive had multiple tranny's behind 350s in the 66 I owned, of them all I preferred the 700r4 automatic with a rv shift kit(for faster and firmer shifting, which in turn leads to longer tranny life) I see these rebuilt at swap meets all the time for 350-500. I would also change the rear gears to a 3.55 or 3.73 set up and it would drive fantastic all around. I did these swaps when I was 16 with no knowledge whatsoever, so I am sure you can with a little looking around find lots of info on how to do it easily. should be a days work and you can cruise in supreme comfort.