Hi John,
There will be no problems associated with using a Fox .59 in a Stuntwagon 60. Charlie Reeves did just that, and IIRC, won OTS at the NATS with his. Tommy Luper, another outstanding OTS pilot has used th eFox .59 with success. Charlie also uses a Fox .59 Long Shaft in the Big Job he published in FM. And I will do the same when I get to build my Big Job (if my buddy ever sends me my Fox .59 Long Shaft! what's three years among friends! I think it is just a matter of slow travel from the West Coast...... LOL!!)
For you purposes "I" would rather use the Fox .59! Be warned, however, IT IS LOUD!!!!!!!!!!
If it is a "long shaft" version, it will benefit from a support around the front bearing area built into the nose ring. Charlie did that on his Big Job. It is a removable thin aluminum plate with an "O" ring inside for the end of the shaft to ride it.
If is the "normal" Fox .59, no such means are necessary. Very easy engine to run, no harder to use than the OS .46LA.
Big Bear