RE: Picco P-zero 0.8cc
Crank passage has more effect on power than strength. The problem with crank size in engines this small using bearings, is that you have to fit a standard size bearing. Bearings are sized in whole mm, unless you decide to design the engine in metric then, throw in an imperial dimensioned bearings.
Timing figures need to be looked at closely to determine whether or not messing with them will change the way the engine runs for the better.
Diesel is an interesting idea. Not all engines respond the same way, but the Norvel .074 made the same power on diesel at 10kRPM as it did on glow at 17kRPM. It would be interesting to try.
If Picco make a special run of airplane engines. It would have bearings. It would need a new crankcase casting. It would be expensive. Picco produced world class engines, not backyard beaters.