Hi, David - I have around 400 flights on my OK Super 60 powered Viking.
In the original configuration with all the spark hardware it weighed 57 ounces and required two ounces of tailweight. Flew beautifully.
When the original silk covering degraded, I refinished it. I moved the engine back .80 inch, put on ultra light wheels and of course, removed the tailweight.
The new weight came to around 53 ounces and it flew EXACTLY the same.
It's a great airplane and in the proper hands, a top-level OTS contender.
I have seen them fly with a Fox 35 at around 45 ounces, various other engines and of course my OK 60.
It seems to fly very well at a variety of weights - BUT, when built very light, beware when flying in heavy wind.
Bob Z.