Magna,
The plane was destroyed by a falling tree last January. I did fly it at full throttle most of the time. You could fly it at less, but the other warbirds I flew with are all going mach3, and you've got to keep up in the pattern. I have flown underpowered planes, and I did not consider it underpowered. I never considered changing engines. It is a fairly streamlined design (like the Zero), and moves through the air easily. I honestly can't see how you could go wrong on your proposed Zero at 17 pounds.

I think that comparing the power to two-stroke, and four-stroke glow engines may not be valid in this case. I built a Dave Platt FW-190 and put a 46cc Poulan conversion in it. It turned a MSC 20-8 at 6500 rpm. The designer was concerned that it wouldn't fly safely on that prop at that rpm. His prior experience with the design was all high reving glow two-strokes. The plane had near unlimited vertical and was very fast. It weighed 23 pounds. The gassers have different characteristics than the glow, and a straight HP to HP comparison isn't always valid. Where you power is developed has a lot to do with it. A glow is a better choice in certain size planes for certain type flying. Look at the pattern guys. Big glow four strokes. They are using what suits their application best. Look at the warbird guys. We are too. Once a plane gets to 80" we almost always fly gas. Fuel is cheaper, cleanup is easier, and flameouts are a rarity. This is especially important as the weight and wing loading goes up when we pile on the scale details.

Just my opinion.
Good luck.