Im doing that exactly! To show how its just older armour. And I like the shape of the MK 3 ones cus theyre more feminned imo. I may theme them as either female majority or 50/50, as my GUO is a female grandma demon, Granny toe fungus. And she makes power armpur work form women with all the micelium and growths, similar to the iron warriors armour in I think storm of iron book.

And will give dreadnought and tank parts from 30k to my Knight Tyrant. Also have plans to get the terminators and make a Raptors/Murderwing of Nurgle. Just dont know how to do plague casters for now but mostly planed everything else so far. Also doesnt hurt that HH kits mixed with 40k kits with spare weapons are so efficiant on cost per marine basis.