I just spent the last couple of hours reading through various LE books, and all I could find was this excerpt:
"... conversion generally consists of boring out the barrels and fitting and soldering a tube in the barrels; the tube being bored, rifled and chambered in .22 inch RF no. 1..."
On a different note, I did repair the handguard yesterday. I cut a very fine lap joint, and used a very thin dowel to pin it from the inside. All wood is still soaking in the raw linseed oil. Three coats, and its still absorbing it all up. Donor wood came from a sporterized smle forend.
Pics of the handguard repair.