I also used a catalyzed single stage black urethane, with PPG flattener added when I painted my 48 F1 Pick-up Cab. It has held up real nice for the past 3 years. The only tip I would add is paint a sample first to see if you have enough flattener added. I had the shop that I bought the paint from add the flattener and when it dryed it was not as flat as I would have liked.

Good luck painting.

Tim