I think the stock Twister works better with an OS .40 FP than with the original Fox .35 setup. The FP is smoother and heavier, of course; the Twister is a bit calmer and smoother performer with its CG moved forward slightly, still completely capable of a fine pattern.
I do recommend having the rudder flat, without the large offset shown on the plan. And the stock wire gear setup is pretty much cosmetic stuff, not durable at all. Lots of people use an aluminum gear with much more happiness. The plan's tail wheel is also wimpy and will not last long. Do something with that.
It's very easy to add adjustable leadouts and a tip weight box with the squared off wing tips. And some people like to add half ribs or even plank the leading edge, neither of which are necessary, the Twister wing works just fine as built per plan.
The older FP .40s are the best for stunt, in my opinion, but the later one also works - newer one has an ABN construction, and sometimes the nickle plating will peel. I suggest using a venturi off the OS .20/.25, it's great for stunt. We really liked the old wooden Rev-up extra wide series props, in fact, the 11x6EW was my choice. These props are flatter than indicated, and the 11" prop loads the engine a bit, which works. Some people add a second head gasket. Our engines were sweet running in the 8500 RPM range, using 10% nitro and 22% oil (half castor) fuel.
The Twister design is one of the best simple profile ships and a great model to learn with and compete with.
L.
"Sometimes something worth doing is worth overdoing." -David Letterman