Surely I'm a bit biased having driven a two-stick for several decades now but you'd have something unique as well as faster on the hiway. Oh, and BTW you can maintain much better speed on hills by splitting the main box, e.g. pulling a 5% grade in third and overdrive at 35 MPH rather than just third at about 28 MPH. At a recent ATHS chapter show there was a tandem axle 46 Chev with a three-speed brownie. Guys were crawling all over it. It was a beautiful restoration. Sitting next to it was an equally nice 359 Peterbilt that was all but ignored.
Ford tandem dump trucks through at least the mid sixties used a 5831A Spicer that has suitable ratios. Grig has one also that I believe he got out of a GMC. The A models have a 24% under drive and a 17% overdirve; at least mine does and it's stamped on the ID plate.
