Tough Decision need advice:

[chevroletrucks]

About 6 months ago I picked up a 1970 K20 with what appears to be a 73-80 something drivetrain. A 350, th350 and np203 to be exact. In the last month I picked up a 75 or so K20 parts truck with a 350 crate motor (less than 10,000 miles) th400 and np203. Then I bought back my old plow truck a 1987 chevy blazer 350, 700r4 and np 208 with 165,000 miles. I want to keep the 1970 K20 as it is a classic, but use the best drive train. This is my work truck and will be used as a utility vehicle plowing, hauling dirt and supplies etc. I really liked the fuel injection on the blazer but it is probably the weakest engine of the bunch and absolutely hated the overdrive of the 700r4. The early 700's kicked in and out of overdrive all the time. The other thing I loved about the blazer was the shift on the fly 4wd of the np208. What would be the strongest most reliable drive train for a seldom driven 3/4 ton 4x4 work truck thats going to be worked when used?