Quoted from G-P-E:China doesn't "make" newly manufactured clones. They remove old EPROMs from waste boards, make them look pretty and resell them as new. For now it seems most work but as supplies dwindle....
In most cases you can mix and match revisions and manufacturers. Exceptions to this are the really old EPROMs that require multiple voltages. You can often move up in size easy enough but you need to look at the extended address pin of the larger device. Does it get tied to ground/+5V? Unconnected & floating? Usually they are tied off to ground or +5V.
For example -- a 27C64 doesn't use pin 26. A 27C128 uses pin 26 as the high order address pin. If the destination board has this tied to ground then you simply copy the smaller EPROM into the larger EPROM. If the destination board has this tied to +5V then you double the image or program the smaller EPROM into the larger EPROM's high order of memory.
You can still buy OTP type memories from places like Mouser but smallest is 32K x 8. Search for AT27C256R-70PU.
These are much cheaper than regular EPROMs (just over a buck apiece) but are not eraseable. If you need to update or screw up programming - you simply toss it in the trash and grab another.
So if I ordered a few of those OTPs you mention from Mouser (32K x 8), I should be able to replace the U49 sound EPROM (16K xfrom Space Shuttle by programming it twice over with the U49 ROM image?