Never seen a girdle on a BBC. Does someone actually make one?
I ran a mild blower application a long time ago with a .030 over 454, steel crank, 2 bolt main, with 3/8" rods even. It made around 800-900 HP.
Kept the RPM's below 7K and never had any issues. Bearings always looked good.
Spend your money and make sure the line hone is correct, and save it on the girdle (if they even make one).