Finally got round to installing the OEM W7 on the home-build. Concerned by the last post, I again called MS, and yes, my previous questions were on file.
I put another issue forward. The student that had started the build, tested it with his XP pro. I put it to MS, that the records would show the prime parts as having been used with another OS. They said 'Don't worry about that.'
I ran the install, and apart from an old sound issue, it went normally. I elected to register/activate on line, and that took some moments, but seemed to work okay. However, when I rebooted, the link to my router was gone. Cleaning up the devices and re-booting, didn't help. A length of yellow wire got me back on't net.
I don't know if I'm home and dry. I won't count my chickens for some time. A pal in the UK tells me that MS's database of internal workings is very detailed. Seems a lot of data to store, but then so many people nicked operating systems, I supposed this is one of the few ways of protecting their interests.