Re: 1972 K20: TH350 or 4L80?
 

Ivr got a 1991 V3500 with the 4L80 and 205 setup..if you can find this setup
It would be the way to go.

Re: 1972 K20: TH350 or 4L80?
 

these trucks have done plenty of work with stock drivetrains, you just need to accept their fuel economy limitations. or go overdrive and realistically never recover the cost in fuel savings, but maybe enjoy the truck more.

i have a 396, th350, 3.73 4x4 with 32 inch tires and it seems just about right. enuff power in first gear and reasonable cruise rpm. if i had more time and money, i would probably go overdrive and put 4.11’s in it. but i think a th350 can keep most of us happy without OD.