Lots of consideration to take into account.

My machine worked well with the original motors, (it was fully functional on 3 phase when purchased). As previously mentioned, I was also very conscious of electrical max demand of finished machine, as well as keeping running costs reasonable.

The 1.5KW version might have been a choice otherwise, as you could just pull the rotors out of the motors and machine the shaft ends down.
Or fit different pulleys, as mine are tapered collet type. Having said that, I could probably bore out originals and broach a key way in to fit those 19mm shafts. Extra length makes no difference on Z or Y on my Interact. Your MDI has a longer X axis cover for the manual handles, so it may make no issues there either.

Only things that may catch you out is the rotor inertia and the possible effect of having so much Torque. ( although you might find a 4NM version in 110ST.

I partly figured that if my 90st 4NM versions ended up being too small in the end, I could always use them on the next project ( cnc lathe).

Guess its all a gamble really. The only good thing ( in my view) is that as they are 220V AC, there is no need for huge power supplies and torriods. Time will tell

Mark.