My order from Stock Drive Parts just arrived. I can tell you all for sure the Lionel gears are metric. Modulus .7, 3mm wide with a 3 mm diameter by 11 mm long center shaft. 13 and 19 teeth.
SDP only shows acetal AKA delrin gears in this size. Delrin is a much better material than nylon but I would preferred aluminum or mild steel.
The SDP gears are not drop in replacements but will have to be reduced in width and sleeved.
I am only passing this information on. I have no interest in going into the gear replacement business.
Pete