[cctalk] DEC Prom MRV11-C and MXV11-B2 ROMS

Is it possible to use the MXV11-B2 Roms in an 18 bit MRV11-C Prom board?  Clearly they work in the 22 bit version, MRV11-D, but I don't have one of those. The intention is to put together a small PDP-11 in an H9281-AB backplane (18 bit) with an 11/23 or 11/73 CPU, Ram, disk controller, etc.