To do it properly you *should* change your master cylinder to get the correct matched type NOBODY does this and I suspect that if you were in a serious accident you could well get fooked over if somone (Unlikley) was to spot that its been swapped out.
Dia and volume of brake components are worked out for a reason. For drum brakes you Generally need to move more volume of fluid in a couple of wheel cylinders compared to 2 calipers hence the huge master cylinder dia.
they both use metric fittings iirc although early discos use hex imperial caliper securing bolts ,and later use bihex caliper bolts
Is there a damper in the brake pipe line by the engine bay in disco ?? This stops the rear discs locking up after apply the brakes ?? Take that out and put it in defender for 4 wheel disc. I think there is a damper I might be wrong
Is there a damper on the disco to stop the rear disc locking up, I was going to do this conversion as well, I have a Disco 300tdi rear axle and was going to fit it to my 200tdi 90. I notice that there is a doughnut on the disco axle output shaft, can the output shaft from the 90 axle be fitted to the Disco axle.
Would the diff flange from the 200 Defender rear axle fit on the 300 Disco axle or do I need to get a new one.