Probably should have started with that sorry ��
No problem there, but it helps. As far as I can see, he needs an mATX board. It has to be compatible with that AMD processor. Find out about the RAM in it in case you need to consult a RAM manufacturer's "configurator" link regarding the motherboard.
Now, given what you say, it IS possible that he's got a Dell OEM case and PSU with parts we could only imagine. But if he were going to do that, I'd think he'd have a different case and a different power supply.
I take it from your response that you want to make it a surprise, so it will be difficult to obtain this other information.
The other possibility: choose a mid-range motherboard, processor and RAM as an entire package. It doesn't have to be AMD : it can be Intel.
You're gonna havta work this out, Ma'am. I think it's a great idea. Obviously your man loves his computers. I hope you get this resolved. 6 December -- the clock is tick-tick-ticking . . .