Not gonna say ya couldn't set up disc brakes on a closed knuckle d27, but it would sure be a waste in my opinion!
You would be much better off I think in mounting up either a Scout II d30 that already has disc brakes, or of course go with a Scout II d44/disc combo. Either axle will be a bit wider than what ya have now, but this is a very popular swap!
If your d27 has the optional 10" drum brakes, those are actual really decent capacity stoppers if they are correctly rebuilt and ya stay with 31" tires or smaller,...even with no power assist.