RE: GP Super Stearman
I printed out the instruction manual from the GP web site and they used an OS 120 single.
And, they provide a neat little plywood box to fasten to the motor mount to put the 18 ounces of lead into, which was needed to balance the plane.
It's all there in black and white, right in the manual.
At least they told you to plan for it, not like some other manufacturers, who never mention that you have to add a ton of weight to balance your completed model.
The Enya, probably heavier than the OS, will require less lead.
The completed plane, however, reportedly weighed less than 14 pounds dry.