Titus-I haven't heard from Verne (Miner 49er) in some time but I suspect he epoxied a truck to the underframe. When I built the Grandt models, I just substituted metal wheelsets for the stock plastic ones using the same mounting as Mr. Grandt intended. I remember epoxying small lead weights to the underside also to help with the tracking. Hope this helps.
____________________ It doesn't matter if you win or lose, its' how you rig the game.