I've got one of these, was going to put it in my one ton, but I sold it last year. But it will work in my rescue squad.
The
Spicer 5831-B Auxiliary Transmission pictured on this page is the one I have, it come out of a 1965 GMC W5500, and as you can see its not really that big. the main thing is to get all the parts off the donor truck, many have gotten just the Auxiliary Box then wonder how they are going to hook it up. the truck mine came from was headed to the crusher at the time, it was set aside to get these parts removed just in time to keep it from being lost forevery.