Wally mart Federal 100 packs are darn decent ammo as said above. Remington Gun Club loads are filthy, but shoot and pattern pretty well. Winchester Superspeed are less than $30 a case, but not very good shells. Cheap blasting though, and if you miss inside of 35 yards it was NOT the shells.
Yes you can use the 2 3/4 shells in the old browning, and it is highly recommended that you do. Shooting clays with anything but target loads is not much fun.