Hi thor3228,
Sorry I don't know your name.
You can use the 601-07593 which was the standard credit unit for the R-74, CTI-1C and R-80 but it is also ok to use the 601-06666 credit computer.
If you can not souce one in your country I still have some in stock.
Regards
Alan Hood
ami-man
UK
alan-hood@datex.co.uk