Well, a 76 model truck shouldn't have been a turbo 4-53 from the start.
So before guessing at a price would want to check the model and serial number on the block and see what that tells us, also would want to see some pictures of the engine.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-