During that era I stuck with Super Tigers and never dabbled in the idea up upsizing a Fox from 35 to 36.
 
Assuming that the bore and stroke of the base engine was .8" and .7",  a .716" crank would bring the engine up to .36 cubic inches, a gain of 2.3% swept volume, which would be significant in a close speed contest.

But it would also reduce head clearance by .008".  If the engine was under-compressed to begin with, this would help.  If the engine was correct to begin with, this would blow plugs and maybe the whole engine.  In that era I didn't know of anybody who was actually measuring head clearance.  But I did hear of a few who were stampeeding buy stroker cranks.

Is there anybody out there who actually bought a Fox stroker crank and got positive results?

The 36x crank was beefed up around the pin. turned out to be pretty durable, even on Blast.  The ST crank on nitro, not so much.

As is I stated, I never either puffed or inhaled the Fox stroker cranks.
But I did spit out a few ST G21 cranks, even on suction on slows. 
I recall doing that a few years ago using a G21 on a SL plane.  It was a treat for the young guys who hadn't seen it before. It was so common that somebody actually put through a rules change to exempt engine parts from the "dropped parts" DQ rule.

36X piston/sleeve/etc into a Fox 35 Stunt: I'm not understanding why anyone would want to go to the trouble?

I mean, essentially a 36X can be had with the 36 "Sport" or "C/L" engine: 36X piston, sleeve, timing, crank timing, hi-compression, etc, in a very light and short package (compared to the length of a 36X), albeit with a plain sleeved main bearing.

Andre