hey darren,
The tech wiki of this forum has alot of info!has helped me countless times.
check this link from tech wiki:
http://datsun1200.com/modules/mediawiki/index.php?title=B310_Strut_SwapCheck under 'Even Bigger Brake Possibilities'
suggestions are:
Volvo 4 piston calipers from a 240DL wagon,
Land Cruiser 4-pot calipers,
GM Commodore caliper,
Nissan S13 rotor & caliper,
MK63 4-pot calipers
of course do more research on those calipers and what suits your needs for the car.atleast its a starting point.Some will need upgrading master cyclinder getting brackets made,using different hubs etc.And if only for street, you would be surprised the difference of just using better brake pads.
ive got b310 coilovers with b122/b110 upper pyros and nismo mk63 calipers.not installed yet but complete bolt on.heres a pic to show bolt spacing,