Derailleur / horizontal dropouts compatibility

I just got a P3C frame and am just stripping my road bike for as many usable parts as I can. I’m starting to think my 105 derailleur won’t fit on the dropouts. Anyone have any experience with this issue? Do I have to buy another derailleur, and if so, what will fit?

BTW: I know putting 105s on a P3C is punishable by death. I’m trying to do it anyway…if I can.

As long as you have a derrailluer hanger you’re in business… No derrailluer constraints with the P3C.

If you do not know the answer to that - please do not try to build the bike on your own. We could not take all the questions, and you could not take all the comments.

Thanks for your advice, Chip, but I would just love an answer to my question.

Thanks for saying what we’re all thinking…

Seriously, building up your own bike is cool and all–but practice on a cheaper frame! One cross-threaded non-replaceable derailleur hanger or bottom bracket could make this an expensive project…

Thanks for your advice. I figured it out. Really, thanks. Couldn’t have done it without you.