Almost all two-stroke glow engines use crankshaft porting. They will not run in the reverse direction unless the crankshaft is ported for reverse direction. Then, the engine will run as well in the reverse direction as it would with a regular crankshaft. The problem is that reverse crankshafts are just not made any more. The demand is so low that the engine manufacturers just won't consider it.
For four-stroke engines, you need a reverse camshaft. Again, they're not available for the same reasons.
After reading the above post, I stopped to think for a bit. [Not a bad idea, from time to time]. I'm convinced that the reverse running engine was a Cox .049 reed valve. The McCoy 35 in the Ringmaster was as far as I can tell crank ported.
I pulled up the manual for my OS Max 40FX engines and looked carefully at the exploded drawings, and there it is, crank porting! Admitting that these engines are NIB, I've never tried to start them and get them to run backwards. But, I'm convinced now that such a feat would be easier than finding a chicken with lips.
Reference the contra-rotating props, further research indicates that it may be appropriate in the case of high horsepower engines with large props, P-factor and such. But with a 1.3 HP engine swinging a 10 or 11 inch prop, who am I kidding besides myself?
Again, thanks for the attention to the question; I learned a lot.
Happy building,
Diggr