WE never made a 403 KTU. That would have been the 4" card version of the 1A1 203 KTU, which was some sort of tie-line, ISTR.
ITT, as Sam has recalled, made a MOH adapter that was numbered 403. Is that what you have?
The SanBar 4200 CO card is the best solution, requiring just a few wires to be strapped in the KSU, and an external source to provide the tunes.
