4 wheel disc master cylinder?

You didn't mention anything about your vehicle (truck?). If you don't have a booster, you want an MC w/ a small bore. I use one w/ 7/8"D bore in all 3 60's Mopars (95-99 Breeze w/ ABS). Many here like the mid-80's Dodge truck MC (rockauto). Both are 2-bolt aluminum, so need a 2-4 bolt adapter plate (ebay) and can buy "plate + MC" for ~$95 on ebay. You may have to re-terminate your tubes if the tube nuts don't match. Don't go past ~2000 unless you want to deal w/ bubble-flare ports (not hard, youtube). If the disk setup and tires are designed perfectly, you don't need a proportioning valve. Otherwise, an adjustable p.v. in the rear tubing is smart, assuming you adjust it in a wet parking lot - fronts skid just before rears.

You can infer the answer to your main question - MC doesn't really map to drums or disks. All the MC does is produce pressure, and the same pressure in front and rear circuits. Old 4-bolt MC's did have different reservoirs for front disk vs drum cars. All newer 2-bolt MC's have a single reservoir for both, so maybe doesn't matter, though there is a wall between them in the reservoir. You might check on rockauto if a different PN for 1990+ vehicles w/ disk/drum vs disk/disk setups. I doubt it, but don't flame me if wrong. Either MC would work as long as you don't let the reservoir run dry on either side.