And, then, there's Northwest Shortline's new Stanton Drive trucks or their 'Magic Carpet' axle drive for O2R. Pretty nifty, I'd say!
I've bought 2 Stantons in HO to convert some early brass EMC Doodlebugs to a decent drive system. Extremely well engineered. Available in a variety of wheelbase lengths, wheel diameter, tread profile.
Another thought for the FWIW repository.
KD