I've shortened a few bbls, and mostly regretted same.
Special purpose bbls for the 870 series are neither expensive nor scarce.
The local gun shop in your area that handles police turnins probably has a few used riot bbls around. Last ones I saw here were in good shape and $75, IIRC.
And, if you take off a few inches from that bbl you have zero choke. Cylinder bore has its uses, but little versatility.