If your putting in a 6 liter ls use the 4l80e that goes with it i am contemplating building a 68 k30 truck it will be a 4l80e with Ord adapter and convert one of my np205s or find a t400 np205 to go with it
A t350 is a weaker tranny then a 4l80e
The 4l80 also has the benefits of a 25 % overdrive gear
Are you going to tow with it work it hard drive it hard ?
Use it like a real work truck or will it be more a patina mall crawler truck ?
Using a rpm calculator 4.11 gear 33 inch tires shows 3 speed auto at 70 mph 3095 rpm compared to a 4 speed auto at 2051 rpm
https://www.differentials.com/techni...io-calculator/