Diesel 67-72 pickups? are there any?

[TP from Cntl PA]

Did GM do like alot of farm equipment makers did back in the '60's and 70's............They'd take a tractor for example, off the line.........Move it to a special department and by hand, install a different engine(Not radically different, small stuff like bigger injection pumps and increased bores and stokes.........larger turbo's etc....... They'd then truck it to a larger dealer and let the dealer place it with a good customer to use and they'd track the progress. After a period dealer would get it back and truck it back to the company and they'd inspect it..........Notes were taken and it was either put back the way it was tested or put back to stock........Then sold again. IH didn't do much of this as they had their own test farm like Deere, but I know alot of storys about Oliver(Later White) doing such things. GM do testing on its own grounds? Or elsewhere like this?

When old Howard told me this, he mentioned the railroads.........Don't know if they bought them, or were doing such a test? Such a thing sound logical?