Try Ford seals for the late model 5.0L V8 or the 4.9L six. They are 11/32" umbrella style and are made of very stable impregnated nylon. The 5.0 GT ones are a little shorter to handle the increased lift of the HO cam - I think they are red in color on the exhaust side at least.
Don't even think of using no seals as your oil consumption will be awful - like 250 - 400 miles/qt. Good luck.
