Bigdog - Just a guess, but I think you will be hard pressed to get 900fps, let alone anything higher. We just got back from a 10 day BP Rendezvous at Hefley Creek, B.C. There, we entered a canon match, which featured everything from small desk-top guns to 3/4", shooting from tables and small carriges with wheels on the ground, to larger 1 1/2" to 3" bores with fiberglass moulding to change them into full size appearing field pieces of Civil War and earlier period.
: The cannon my team shot was only of 1 1/2" bore, not much larger than the 2 bore that Steve is building for you. We shot a 1.35" ball - very little larger than a 2 bore ball, with heavy patch and with only 300gr. of powder. This rocked the heavy gun and carriage (perhaps 600 pounds) back on it's wheels enough than that thought of shooting such a calibre from the shoulder would not be entertaining for the shootist, me thinks.
All my best wishes to your next of kin.