PPG and many others make a high temp reducer. Many call it slow-dry and if you look at the "ingredients" you will see it is a different animal. If there's a chance you'll be painting at 80 degrees or above, I'd use that. All it does is to allow a little more time for your paint to lay down and flow. Slower drying can help you avoid orange peel. Good luck!

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end