Jay, the way I see it is that your approach is the ultimate after-market full-replacement drive upgrade, while Bob has refined the original Weaver/P&D chain drive setup to the leading edge of what's doable. I've shamelessly copied both your ideas!
As well the Finescale 360 chassis is useable in both scenarios and has the benefit of ditch light wiring channels and machined-in side frames over the Des Plaines brass chassis. But it's lighter hence the supplied weights. Also Kelly's adjustable drive towers help in fine tuning the original chain drive.
The only thing I would add to your most excellent solution is the Tang Band 1925S speaker module which I learned about from Bob's work on A&O locos. Not sure if you've tried that yet but from my experience it's a massive sound improvement over any of the regularly used "O scale speakers".
Thanks for all that you do for O scale! 
