Mine are Fosseway four pot calipers and vented discs. Rears are XJS Jag.
I have seen others used, but are mainly Land Rover (IIRC?) and modified transit discs. Also, there was someone making up distance pieces so you could use the P6B front calipers with vented discs but I don't think these would stop better, just be better against brake fade.
My solution was a pair of Outlaw racing alloy 4 piston calipers from the States and redrilled pcd vented and grooved discs from Vauxhall Omega. Calipers bolt straight on but I needed spacers to get the disc centred. They come with stainless pistons as standard and
are super lightweight.
Wilwood do very similar offerings.
The calipers were around £100 won on eBay, discs won for 99p machining work £30, pads around £50.
All still untested but they have the makings of a strong setup