Don B, to your post #9...
The magic number for reversing rotation on an engine with a detachable front end (bearings, shaft, inlet) (that has a symmetrical bolt pattern allowing rotation by 90° either way) IS 90°. Which way doesn't make any difference.
The intake port in the case gets turned 90° and the shaft port meets it the other 90°, earlier or later. If you turn the front end counter-clockwise, you could call the change later in the stock direction of rotation, and vice versa: CW could be called earlier... Either way adds up to 180°.
One problem: the shaft port timing is often 'biased' to run better in the originally designed direction. Reversing the sequence in which the ports open will reverse that 'bias' opposite to what the mfr intended. For mfrs who offer either CW rotation engines (e.g., ENYA for several engines) or CW shafts (e.g., FOX), it is safe to presume that the mfr mirrored the port timing bias to get the same advantage as the original CCW rotation shaft in CCW operation.
BTW, I've never seen a COX engine with a front end suitable for this trick...
I HAVE seen COX reed valve engines run happily, and equally well either way - occasionally when you DON'T want them to... Reed induction is "controlled" by pressure changes in the crankcase, not by carefully timed ports cut into the metal (or plastic). Most reed COX engines don't have the power of a decent Medallion, or anywhere near the power of a TeeDee, but a reed at the back of that Do-335 could be a simpler way to do it.
The "product" engine - as installed in the department store plastic ARFs - isn't as bulky as the "integral tank" reed engines, and you'd use a separate tank. That could make fuel feed easier to tune in for an engine flying "backwards."
The old side port (usually spark) engines could run either way equally well, except that spark timing prevented reverse running...