Aaah, thank you, that is helpful! Yes, with frame I meant the pickup surround. Sorry, my English is probably awkward, it's been a while since I left school ;-)

I thought Humbuckers and P90s had the same shape, so my bad. Let's see if it fits. If not, I'm just going to keep it for a possible future build. I don't think I have the skills to enlarge the cavity, that screams trouble pretty loud to me.

Good tip with the multimeter, I actually have one.

Now it brings me to the next question. I have A + B 500k pots. How do I find out if I can use them with the pickups or if they need other pots? Or do all pickups work with the same pots?

Thank you so much for your help so far =)