I've done some work on modding AEG barrels to fit the WA M4 but I have not done any for WE M4 as yet, but I can tell you it would be simpler as less precision and material will be bored out.
The last picture below was a Madbull PWS barrel for an AEG, I chopped the end off with a mitre saw and used a 1" diameter shank to bore out the center with a drill press, in your case with a WE you will need to remove material for the brass sleeve to fit.
For the WE outer barrel, you will need to:
- Machine the end off
- Widen the diameter for the collar clearance
- Drill two holes at the 3 and 9 O'clock positions and insert 2 roll-pins, this will act as the 2 protruding notches you find on the stock WE barrels.