
with Jonathan and John....
..... to clarify, PNM take Hi-Spec Billet-4 callipers and have them re-branded with their own logo - you get the exact same kit, but pay a few quid more from PNM as they make a cut on the wholesale price. Some may say that it makes them untenable, as why not go direct to Hi-Spec and save some cash.... the answer is in the 'customer experience' that you will get - you pay a small premium to get them from PNM, but if you have any problems, they will answer their phone and sort it out - quickly! Hi-Spec have a history of taking your order (and money) and then having delays after delays and when it all arrives, it not being quite right. They will sort it out eventually, but if it were me, I'd pay the few quid more.
Wilwood, being an American company, was the option used by Brian when he first looked at a brake upgrade, as he is based in USA! The callipers are all available off the shelf, as are the rotorz - the bells were custom-made back in the day, and when they were gone, they were gone - unless you find a second-hand set, it is only viable if you can locate a set of drawings (which I've never seen) or can create a new item from scratch, or reverse-engineering one that someone will lend you.
I have always said that a well-maintained OE set is fine - even for track use (with a decent set of pads), but I have Hi-Spec on the car I'm currently restoring, so will be keeping them.... but I wouldn't spend £500 on a set!
The whole issue is that there is insufficient space inside the 15" wheel to do very much in the way of disc increase, so once you have 'better' callipers, and 'better' pads, that's about it - until you fit larger wheels.... the rear is a completely different story, as a huge increase (to match whatever you do to the front) is possible by changing the pressure limiting system, or fitting bigger discs, or better callipers (not necessary unless you have an issue with the current handbrake) etc etc.