Personally I'd go for a motherboard that started with 7 instead of 6. Those part numbers rise over time..... later is better for you, I believe.
There are many posts here related to your issues, and you can filter in the top left search box for "Z620 motherboard" or Z820 motherboard..... there is a lot to read, and more in there on the Z620 but those two workstations had exactly the same issue with the revision 1 being needed for use of v2 processors. Leave the default for searching this forum only. Originally HP was also going to activate the older Z620 and Z820 motherboards for the v2 Ivy Bridge processors, but they changed the motherboards enough that it just did not make sense to them. This is unlike with the Z600/Z800, which also had original and a revision 1 motherboards. In that case the main chipset actually underwent a sSpec revision from C1 to C2. Not so with the Z620/Z820... other things changed.
Remember that there is a difference between Assembly and Spares part numbers. PartSurfer only uses one type, and I can never remember which one it is. Thus, the same motherboard will have two part numbers....... AS# and SP#. I think that the one that starts with 6 would be a risk for you.
Here is a good review: Link
The latest QuickSpecs for the Z820 list the v2 processors that "require" the 1125W power supply. Your processor is not in that list, they are all higher powered ones, and we've got a Z620 using that processor and the regular power supply. So, you're safe on that issue, thankfully.
Maybe try PM to Skylarking through the forum.... he has some tips, and you'll find him via the search above. I've dinked with that a bit, but he knows much more than me on that process. I used that to get in the proper serial number for a couple of brand new motherboards inserted, xw era, but he has worked with the Z era with that. Probe your current motherboard for all those numbers and codes once you get into the service mode. I don't know if you can change the UUID, or would need to (probably not). W10 activation, however, is based on UUID harvest by MS so you'd need to reactivate if you change your motherboard.
If I have a chance, and probably won't, I'll dig into that revision 1 Z620 and see if I can spot the actual part numbers from the motherboard itself. Doubt I can get to that.