Just a thought...I also have a Williams brass 611 with original motor and gearing. I converted mine to BPRC using a 12v 2000mah NiMh battery and the Deltang receiver is either 3 or 6A max (I'd have to open up the tender to be sure which Rx is inside), but I've never had it stall yet. When I first had the idea to BPRC it I measured the current and seems like it was 1-1.25A max and I know I have pulled at least 14 unlit passenger cars with it.
All I have wired in are head and rear lights, no markers or class lights (yet) and no sound or smoke. Sound doesn't soak up a lot of amps anyway, don't know about smoke because I refuse to use it.
And yes, the paint job on the J is glossy not flat. My Williams J has a rough paint job on the nose, I believed caused by heat from the old bulbs used.
Excellent job by the way