Thanks everyone for the responses. My previous experiences with impact wrenches haven't been very good. Seemed more like a toy than a tool. But I had only tried battery powered ones that provided only a couple of hundred foot-pounds of torque. Here's an air-impact one for a hundred bucks I found with a 3/4" drive that will put out a thousand foot-pounds so maybe I'll get one of these.
I already have a 135 PSI compressor and a set of 3/4" sockets, so I'm already more than half way to a solution. All but one of the reviews written about this one were very positive, but if anyone has one and has a complaint, I'd like to hear it.