RE: Soviet made U/C airplane, engine size?
Jens,
I tried to respond, but timed out (?)
Go with Jim Thomerson's ideas.
I don't know cyrillic characters, but the large wording on the box looks like it would sound like something meaning Model Monoplane. I can't read the small print. If you read Russian, or know someone who can, more information might be right there.
\BEST\LOU