Steve, I'm currently using my 1.80 on the new 79" WS Great Planes Cap 232 - part of the same series of your Yak. I've got about 15 flights and couldn't be happier w/ that combo.

I've run both the Meijzlik 18x8 and APC 20X8 (narrow blade) with good results.

An idea regarding the DPM versions might be to ask Dave how compression rate was reduced. If they shimmed the head (instead of machining new ones), then all you'd have to do to run FAI fuel is removed the shims! As a last resort, you could buy a replacement head from Just Engines, but my gut feeling is that the engine will run just fine on 5% nitro.