Lot of trouble for a 20% decrease in engine speed.

On a 3/4-ton truck I think you have better options. On a 4000 series or bigger truck I think they make a lot of sense.

You'll need to mount it, modify the driveshaft and create a shifter, but none of those are a big deal, right? The only ones I've seen available seemed too expensive to me, but I've sure considered that option.

Find out what model it is, if it was designed for a smaller truck it might work for you. If its one of the really heavy models you may add more weight by time its mounted than the reduction in engine speed can justify.

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...