Denny,
I did a "restore" of my Dad's old Cub tractor last summer and since it's a worker, I went ahead and painted it with PPG's Shopline paint. The epoxy primer and single stage urethane color run at least half the price less than their top of the line stuff. Although I'm no paint expert, I really couldn't tell much of a difference between the Shopline stuff and the DP epoxy and Concept urethane I used on the 51. The Concept color may have a little more solids to it and some other stuff, maybe UV protections and the like, that makes it cost twice as much, but I've used the tractor all summer and I'm really impressed with how well the paint has held up. It sprayed real nice, color sanded and polished up as good as anything I've used, and has been very chip resistant.
Bob
