Hunter Arms Company had a saying "anything within reason" and your gun would be within reason.
First you could weigh the barrels and compare it to another 20 ga with 26" barrels, the stock could be drilled out and left without fillers. Look under the butt plate, lastly remove the locks and see if there are holes drilled in the long arm of the receiver. The barrels could have been struck thinner so be careful of that. The chambers should be 2 1/2" and if changed to 2 3/4" from the factory should have a stamping on the barrel flats stating so.
I would have the barrels wall thickness checked to be sure it is safe to shoot.
Sounds like a wonderful gun and good shooting with it.