Welcome to the forum, but you are in the wrong area to ask a question about your setup. I would have went to the turkey gun section. You are posting in the choke tube classifieds section.
You will find darned near every bit of information you will need on "Old Gobbler"
You're 28" will be fine. That part is personal preference. You definitely want to find a tighter choke for your rig. Make sure that you find a choke and shell combination that will produce killing patterns at known distances. There are some chokes in the classifieds right now that will beat the tar out of your Improved Cylinder. Clean your gun, get some big pieces of paper \ cardboard and shoot at a dot to make sure your point of aim (POA) and point of impact (POI) are in sync with each other. Good luck this season.
