Even if you can find an early 2-rail version, it would still have the twin vertical motor "China Drive." One project that I never got around to, was turning an MTH AS-616 into a four-axle AS-16 using the better-performing central motor drive and AAR-Type B trucks from an early-1990s Weaver Ultra Line Alco.
The drive parts are still available from P&D Hobby (now online only.) Depending on the railroad you model, and whether you would accept a 4-axle prototype, this would net you a better runner without having to hunt for a potential unicorn. My $.02.
