You can use the original RS master cylinder but need to change the fluid reservoir to one from any other mk4 Escort (got mine from a scrappy for £5) or you can just block off the plastic return pipes on the original reservoir!!(this looks crap tho)
Both modulators need to be removed off the gearbox and all the pipe work associated with them! You can then just re-join the brake pipes correctly underneath the car although you will need to make up one small piece of pipe!
To do the conversion you will need 2 caliper mounting brackets,2 brake calipers for solid disks,2 solid disks(i used 253mm ones from an xr4i)2 brake flexies and a handbrake cable! most people use a cable from a mk5 rs2000 but i had a cvh cable modified to do the job!
As regards to MOT's, when the tester enters the car details into the vosa computer it WILL tell the tester that the car has an ABS system and how to check it! the easiest way around this is to bridge the connectors in the engine bay and the warning lights will work as usual!