David,

It is quite a while since the disc brake adaptor plate was developed but I have a feeling it was needed because the MGA item positions the caliper awkwardly in the wheel arch (but I may be wrong).

The other issue is, of course, cost. Even if you have MGA calipers, the availability of parts for the MGB is better and cheaper. The MGB caliper was also an enhanced design. For instance, they do not retain the central spindle in the piston, which was found to be superfluous. MGA owners often break them off and use MGB pistons.

The hoses are different so as to get the right length. I think the MGA ones are a tad too short and risk getting stretched on full lock.

Malcolm

OK I appreciate a calliper carrier is needed, and an MGA one will obviously fit the MGA hub ..I have access to MGA disc & calliper rather than the MGB Route!
david

I’m sure someone will be along to correct/add but in the meantime my own experience is:
1) MGA hubs for disc braked and disc-wheeled cars are a bolt-on necessity BUT they are like rocking horse manure. A viable alternative might be the MGA hub for wire wheels as they are remanufactured but they would restrict you to wires which are also expensive.
2) Either way you will need a carrier for the caliper, there is an MG supplier on Ebay who sells them ex-stock apparently, from the photo they seem to be the Green-type and should also bolt on.
3) This enables you to use MGA discs and MGB calipers. The MGB hoses have the correct fittings at each end, their only issue is that they are a tad too long.
Servos/reservoirs/residual pressure valves are often discussed but as yet never resolved. Best of luck!

Am I right in thinking that disc braked MGA front hubs bolt straight on to the ZA&ZB & that you can then use the MGA callipers & discs without modification. If you want to use MGB Callipers & Discs you need an adaptor plate & suitable (different) hoses?