it should be a cast drum. And where are you pricing a converter? Make sure your not looking at an AodE converter. The aod's really don't have "lock up"..
I recently had my AOD rebuilt by Tualatin Transmissions with a 2000rpm stall torque convertor, external cooler and trans-go stage 2 shift kit. If I were you I would take it to a tranny shop and have them rebuild it and warranty it. I'd spend the $100 and get a trans-go shift kit (I'd go with stage 2 or 3) and a 2200rpm stall torque converter. The shift kit is very mild and shifts how the AOD should have shifted from the factory. I believe AOD's came with non-lockup although I have read otherwise. I had no MPG difference with a non-lockup converter.