Radial mount won't be plug and play. Google radial mount and you'll know how the fitment is like. You still need to make a bracket but a radial mount bracket is easier to fabricate and adjust to make the caliper fit.
I'm not sure about e34 la cause i dunno what OEM rotor sizes they have for e34. Cheapest alternative is to find what bigger rotors from other BMW models that can fit on the e34, then from there you can figure out what calipers can fit those rotors. That way at least you won't spend a bomb buying new rotors every time.
Both me and Kenneth (whom you met last week at TT) have porsche calipers on our car. Mine is from a Porsche 986, whereas Kenneth's is from a Porsche 996. Both use different rotor setup but Kenneth's setup has the option of using 345mm rotors from the E46 M3 CSL.
Mine I use the E46 330 rotors which is 325mm.