5 lug mgb brake

[mgb260]

Robbie, For your setup the small Mazda RX7 rear caliper is about right (you would also need a thinner rotor)for balancing out the small Toyota or Mazda front calipers. The GM rear would be a good match for the large Toyota front calipers . Like the larger Jag rear brakes would balance out the large LS Chevy front brakes for Jim.

[classic conversions]

Keep in mind that cylinder bore and brake bias are very important. regardless of what heavy light caliper you use, either front or rear.
Piston dia of caliper front and rear, MC piston dia , bias of brakes and pedal ratio, weight of vehicle just to mention a few.
 Just replacing calipers with ones that fit is a gamble.