Be prepared to make a lot of jigs in this conversion. I did one for a 16 gauge FWE that the barrels were cut to 26" and are now bore/bore. I used a radial arm drill press and a 15" drill press to drill the holes for the split extractor pins. Plenty of careful measurements. The radial drill press came in handy putting the ejector activator pin in.
If you go to the DYI page 14 on the DGBBS you will see what I did to make this happen. Plenty of careful measurements.
Here is one picture of the process.