Er, sorry for asking such a silly Bubba question, but couldn't you just take a four inch section of a shot gun barrel, split in half like a canoe, and put about 1/2 inch of JB Weld in it, and then just push it gently onto the underside of theRossi  barrel, wipe or cut off the excess  paste around the outer edge of the split piece, and then just let it set up for two days?  
   Wouldn't that give you a solid  hanger you could tap a hole in, to mount the  forearm?
   Just askin.
Mannyrock