So I finally got over there to take care of this customer. I asked him if he wanted me to remove it and he said it didn't matter if I felt it didn't need to be done. So I took some advice in this thread and used the existing feeder.
I removed the 50A receptacle and pulled the cable down into the crawl space and landed it in a 411/16ths box and pulled 12-2 romex from that box to a spot above the countertop just to the left of the stove. That's another thing I've never done, but the counter space had no receptacle and the stove cord reached to the location, so there ya go.
Did everything like you guys said. Pigtails, re-identification, new breaker, the existing cable was all copper so no problems there. I did leave the old breaker in there to take up the space.
Anyway, thanks, it saved me the trouble of running a new wire through this crawl space which would have been a nightmare. It's clean but is currently being used to store anything and everything his wife saw at the Christmas Tree Shop or wherever. Wouldn't have been hard, so much as tedious and I don't think he'd want to pay me $450 for one plug.