I got hold of this beast today - you're right, the mounting pattern is VERY long on each side. Its also locked up solid since its been sitting on a shelf in its box for probably 40 years and the factory test pop oil is completely solidified, so its going to need some soaking and prodding with a heat gun to loosen it up.

Looks like a pretty stout engine though. No instruction sheet in the box. How did you break yours in? I'm thinking something light like a 9x4 for running on the stand and I just mixed up a batch of ~26-30% oil 10% nitro fuel.