If the minor diameters are at keast the same, you can cut 20 TPI over the 28TPI.
If the original could take 1000 foot pound of torque without stripping, the cut up on could take ~~ 500 foot pounds, and you only need 100 foot pounds.
But it would be so Mickey Mouse, I doubt you could get a real smith to do it. You would need your own lathe and a sense of humor.
Here is a 17" barrel for $35 + shipping. I have had good luck with them.
I can cut 9mm chambers and throat with just a drill set.