Thanks.
My eventual plan is to be able to record these engines myself, simultaneously inside and outside the cockpit, rather than search for freeware sounds to remix for AHII. Granted, the equipment won't be cheap (wide diaphragm vacuum tube condenser microphones fed to a vacuum tube power amplifier which itself feeds to a laptop mixing station), but the results would be phenomenal. Of course, using such hardware, every recording would be referenced at 32-bit, 192khz stereo, kept in a secure archive from which down sampled, remixed copies could be made.
Once everything is mixed and packaged, I think it would be entirely acceptable to make the sounds free for everyone. Think of it as a kind of museum format, where anyone can experience what it sounded like for the pilots who flew during the war on all sides.