First, forget the .049's and the Gilbert .07. Matt Kania designed the kit for a .15 of the mid 1950's. The .15's available during that time included the OK Cub .14, K&B .15, Cameron .15, and finally the Fox .15. They were just starting to import foreign engines.
As you have surmised a good .10 of today has more power than those, and because of the muffler, more weight. If you put a .15 on it you will probably need to add tail weight for an even higher wing loading. I would go with the .10.
Of course your plane, your choice. Good luck either way.
Hi George, Those models will fly well with a LIGHT weight .09. The Ringmaster Jr
showed a Cub .099 and a Torp .09 and a Torp .15 engine on the original plans.
My first Ring Jr was powered with a Cub .099. The Cub weighed only 1.77 ozs.
It flew very well on 35' X .012" lines. It actually was full pattern capable; but
that was in 1954, so I wasn't. A friend of mine flew a complete stunt pattern
with it in 1956. This experience prodded me(over 35 years later) to start using
smaller than suggested engines for the Jr. My first smaller displacement model
used an AM 10(1.0cc) diesel. It flew magnificently on 40' X .008" lines. The next
models used PAW .049 diesels, I did cut a bunch of pork by slimming the
fuselage, reduced stab and fin area and subsituted the empannage with "C" grain
3/32" sheet. Oh yes, I shortened the nose to accomodate CG and tank size.
The PAW .049s have more power than the AM 10 and are a bit lighter. The Paw .049
will fly a stock Jr with careful attention to weight and wood choices.
My last two Jrs weighed 7.125 and 7.25 ozs, ready to fly sans fuel. I don't remember
what my 1954 Jr weighed, but my late 1980's(stock kit) AM 10 model weighs 9.8-10.1 ozs
depending on prop used. I fly the latest Jrs on 44' X .008" lines. Yes, I agree to forget
about using his .049s and the Gilbert .07.