I believe a popular brake upgrade[for the bigger engined Capris at least]was to fit the front calipers from the BL Princess.
It had real problems:
the caliper was designed to go under a 14" wheel, so you had to grind the top. The castings were variable, which made many of them dangerously thin - after one of mine blew the seal out, we all reverted to M16s
it's meant for 257mm diameter discs but Capris are 247. Chamfering the edges of the pads isn't a particularly good solution....
The Capri's brake problem isn't a poor caliper, but the inadequate 247x20mm thick vented disc. If you fit a bigger caliper and aggressive pad to them, they last about 5 minutes. And you regularly boil the wheel bearing grease.
They're bloody heavy!
These days the calipers are outrageously expensive, and there are better options. The RS Turbo 260x24 vented disc needs the hub circumference turned down slightly and the disc mounting ears removed, and brackets to fit the matching caliper aren't difficult. That gives a suitably improved disc, that's now clamped between the hub and aluminium wheel which acts as a good heat sink