From what OC wrote, there were 15 frames made and 10 500s sold. Now one or 2 of those unsold frames have been accounted for as well as 5 or 6 500s. But OC may have new information concerning all that, but that is what I last read.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90