Hi Hot Water:
I have also ordered 3rd Rail's CB&Q O1a Mikado but in #4978 with the Elesco feed water heater. Prototype #4978 is on display in Mendota IL & love its appearance. I think that the #4960 had the Worthington feed water heater. It is great that 3rd Rail has offered the model in 3 different road numbers with matching details.
Lionel's Mikado above is an O4 USRA design.
This is a great time for CB&Q steam on O-gauge. Enjoy your models when they arrive !