Paraphrasing from the wiki: The antigen you select affects the polarity slot your vulpaphyla starts with and the appearance of its head/neck. The mutagen affects the resistance type and the appearance of the tail. Even if you don’t have all the parts you should be able test out/see the appearance and stats/descriptions of any combination to see the results. Just proceed as if you did have all the parts ready.
With all that said, like the others have mentioned, when making any of my infested friends, I did so with a focus more on appearance than stats. Tbh imo, the stats don’t really make too much of a difference unless you have specific mod configs or fight against certain factions more than others.
My lich was named Zuu Imuh (don’t remember the spelling) before it changed to Oghh Rikk.