Pipe,

You're right about the reasons for "odd -ball" scale, at least in the old days.
We scale nuts had to build to engine and accessory sizes that were available.
Example, in the late 70's Webra came out with the first .90 in engine. I had been drooling for larger displacements so i could build bigger planes.

As soon as I got one i built a 1/5th scale Mig -3 and published the article in FM.
Soon after Dave Platt came along with "Stand -off Scale' and then Giant scale.
he called me one night and asked about the Mig and was kind enough to say he thought I would get credit for moving us all into bigger airplanes.
We all found out quikly they flew better, looked better in the sky and could carry more weight and thus more scale detail.
I took the Mig to the International Scale meet in Dayton in 1975. The Russian contingent there loved it and we spent a rainy afternoon in the scale judging hanger talking models ( through a translator) and eating Oreo cookies which they asked the receipe for. Since I thought that might be divulging secrets to the enemy, that night I went out and bought them a large package of Oreos.
The result was some good pen-pal friendships and alot of traded model info.

alan