You don't have to do that. Only Series 400 HP "Apollos" had both HIL and Domain keyboard connectors, and all Series 400s will run Domain/OS. Even though they're post-buy, it seems as though HP did put some work into them - my 425s is well-built and has pretty much everything you'd need to get a good system running without looking for parts (SCSI and Ethernet onboard). The downside is no ATR if you need to have it talk with older boxes.