It seems nobody has any advice or comments. That's ok, I'll try it out the way I planned and report back with the results, maybe it will help someone else. I received the brushless motor and coupler today (offshoreelectrics.com has incredibly fast shipping!) but the ESC has not arrived yet. The brushless went in without too many problems so the hard part is done. The brushless motor is noticeably heavier than the old 550 motor, hopefully it will make up for it in power and efficiency.

What should I lube my drive shaft with? It is a solid 4mm stainless shaft in a brass stuffing tube. I tried axle grease but it was way too viscous (too much drag). Then I tried gun oil but that seems too light.