Neil Johnson and others may be able to cut you an Eprom at a reasonable price - I still keep meaning to forward details for my K4. NOTE: IIRC 1.4 is the current max for this. And the K4r is different ROM to the K4. Clearly you have a K4 -- the keyboard being the dead giveaway.
On that note, I had problems with my keyboard. I took it apart, cleaned it, works nicely. However, what stops the keys from rattling around laterally? I see you have taken your keyboard apart - do you have any pictures on the mechanism that you can share before you put it back together?
I was expecting some form of Teflon bushes or something - as it stands my keys are more crooked than Cletus Del Roy Spuckler's teeth!!
I quite like how the channel aftertouch responds - but since I trigger most stuff of my GEM s2 it doesn't really bother me about my crazy K4 keybed - but would be nice to fix it
Regards
Steve Hookings
PS the volume control seems to have little or no effect. I read somewhere that a cap may have blown?