First get some faster gears for your rear axle.
https://www.stovebolt.com/techtips/axles/1%20Ton%20Upgrade/Another option is a 5 speed overdrive. The NV4500 would be a good choice. A T5 would also work but is kind of light weight in comparison.
The auxiliary will be heavy, need crossmembers and mounts, shifter, and both a new and modified driveshaft. Plenty of work and added weight, possibly expensive depending on your luck finding one and how much of the work you can do.
Don't choose an auxiliary transmission because it's a smart choice, because there are easier ways to go faster. Do use one if you want an auxiliary just because, they are interesting, unusual, and functional.
I have a 4 speed auxiliary on hand for my 1 ton when time allows.
