That old Poly Choke will work fine. I set mine at MOD and have at it. I have a brand new installed Poly on my 16 Mossberg 500 and I have shot factory steel #2's at FULL with great results. Keep it clean and don't tighten her down too much. It won't hurt but you will likely hit more on the MOD setting. I have no experience in shooting steel shot bigger than BB through a Poly Choke so I cannot say if T and F steel is OK. Most of us don't have any real use for that big steel anyway. OK I know some goose hunters will chime in about T and F but they likely are not shooting a 2 3/4" chambered Poly Choked gun.
Darryl