DES
The answer is yes and no. Sort of!
Lee Shaver will, and has, mounted the lug from an existing barrel to a octogon barrel of the owners choice, and fitted it to the rifle. I'm sure it was pricey though. There is another smith that does a similar setup but he drills out the old receiver stub and fits a new barrel to it.
Both cost more than a new Handi.
There is a smith I have found that will bore and chamber existing barrels to a non NEF caliber. About $200 and six months of wait.
