Worst case, you could pull the old plugs and try to clean then up, regap, then reinstall. This is assuming of course that you don't ruin one of the wires on the rear bank when removing it, lol... Which judging by the sounds of it is highly likely. You may be able to get away with just cleaning up the front 3 and see what you get.

Whatever you do be gentle on it and don't drive it anymore than you have to. Last thing you want is a chipped piston or a dead cat converter.