Hi Bruzer
Sounds like something I did a couple of years back. I have a heavily tapered octagon 20" barrel but left the mag tube factory length. call Regan Nonneman and ask if he has any 22" marlin barrels in his take off barrel bucket. He always does, since he makes custom marlin octagonal barrels. He'll mill one octagonal for you at a very reasonable price. Have a local smith screw yours off and the octagon one on and your done at a fraction of the cost of having him make you one from scratch. My first one was an XLR barrel he had on a stbl I had and it is the best balanced and shooting rifle I have ever owned, and I've had quite a few.
If you send him the rifle it might take many months to get it back Lj
