4 speed or 4 speed OD?

67Dart273 said
Keep in mind that lower and lower rear gears means you re-HEALLY need to pay attention to shaft balance, U joint condition and angles. "Memories" LOL of my Jeepin days with some of the guys runnin' 5:38s and OD. Ye.....you can do 70, OK, but that shaft down there is REALLY turnin'

Exactly.

My philosophy with overdrive is to run a low rear end gear to keep driveshaft speed minimal to make the rear end and u-joints last longer.

You have to decide if you want to race or cruise. OD will be good for a cruiser, 4 speed for a racer...