I'm no help, but this reminds me of buying my first big engine. I had my eye on a Berkeley Navion kit. The box listed the applicable engine ranges for free flight, RC, and CL. .29 was common to all three, so I went off to the hobby shop with my lawnmowing money and got an OK .29, an machine whose only use was converting methanol to noise.
It reminds me of yet another .29 historical issue. Hey, Paul, who was the kid from Detroit who used a Supertigre .29 to win Jr. combat at the 1964 Nats?