I am running 10-12psi on the stock BP CR I think it's 9:1 or 9.4:1? No problems. I am running it with XR2 electronics
The Kia was OBDII wasnt it? That would be a hell of a mess to swap into the Capri. I'd source an Escort/Protege harness, ecu, distributor, etc and use that - comparatively easy to wire in. Unless you're really up for an adventure
Megasquirt would let you keep the electronic ignition.
This question might get more detailed answers at ClubProtege, they are much more knowledgeable on the different flavors of BP