I swapped the TBI system from an 88 K5 onto my 79 k10. I used the entire harness, engine and everything from the blazer. I modified the blazer sendingunit to work in the truck fuel tank. All in all was a pretty easy swap, I dont know if it would make sense for your location though, as I am unsure the availablility of parts. an aftermaket system might be a better way to go.
I havent driven mine other than around the farm so I have no idea on mileage, but the drivability improvement was my main, goal more than fuel economy. I would expect you would see some improvement, but it is hard to say.
