The good running qualities stem from use of Atlas SW8 trucks with "gear cassettes," IMO the way a model diesel SHOULD be built. After all, two million HO and N scale railroaders can't be wrong! He used a better motor than Atlas did (it's not hard to top a Mabuchi RS-385), but no flywheels. I would recommend the use of dual flywheels.
I always thought it was a pity that Atlas didn't reenter O scale with a GP-7. Then we would have had the correct axle spacing and Blombergs to use under F-3's, F-7's, GP-9s, CF-7's, etc. Because they started with a switcher, the opportunities for reusing their trucks / drive are limited to locos with AAR-type-A trucks
Overall this scratchbuilt Baldwin is a very impressive effort. Thanks for sharing!!