I have a 28" vent rib remchocked 870 that I dearly love. However, it would be really handy to have that barrel at a 21" length for rabbit and squirrel hunting (since that is what I use it for). Is this something that can be done while retaining the vent rib and the remchokes? I know that you need to have a good smith thread a barrel for chokes so that it will shoot to point of aim. If this is doable, who would be able to do it? Thanks