Mike, IMPORTANT point: you can´t fit a magnet into my chassis!
What wheels / axles / tires / rubber do you want to use?
If i should make a suggestion, go to Ranch-Design, use a Fyrebox-2 motor (shorten the motor axle), 8 tooth brass pinion, 28 tooth Ranch-Design crown gear, front tires WDF17109 .395"x.187"x.094" Double Flange Wheel, rear tires WDF18089 .395"x.312"x.094" Double Flange Wheel, both with Low Profile Tires, .094" Dia. Axle. Get also some high flex guide wire from Steve. Desoldering braid from a hardware supply for braid.
you will need a .094" drill bit to drill out the axle holes in the printed chassis.
cheers,
Peter
p.s. did you think about trying a ranch-design inline kit chassis with rolling kit? got a magnet pocket!