Neither the 230 or the 235 will have the power needed for highway driving with a 3.07 gear. Your best milage would be the 230/th350 with a gear in the 3.40-3.50 range if you want to go with an auto. It all depends on what you want. I have a 350/th400 with 3.07 gears in my 69. Just put an advance kit in the hei, upped my milage from 12 to 16. Lots of power, especially above 60. All three of your engines are very dependable. The th400 tranny is as bulletproof as GM has made, the th350 uses less power but is still good. To enhance the life of either one you can put in a shift kit, which makes a bit harder shift, but prolongs the life of the clutches.
Trying to figure out what gear is in your truck. Original would have been either a 4.10 or 3.73, I believe, if it's a 1/2 ton.
