Hi Bob,
The 29 R won the NATS in, I believe, either 1957 or 1958. Think it was a single plug version though. This was a few years before I became active in CL speed flying.
In 1965, Fox sent two of the 29X RR motors to Dub Jett for evaluation. We put one of them in my B speed ship and test flew it on the circle behind the L&H Hobby shop in Mesquite, TX. The speeds we obtained were a bit down in comparison to the Super Tigre G21/29 motors that I was using. I recall that I was impressed with the fit and finish on these motors. We might have coaxed more speed from them with further development but I wasn't involved in any more testing of them.
Mel