I installed the above 603-121 pressurized tank with the Stant radiator cap. I modified the lower return opening by removing the brass sleeve and tapping the hole for a 3/8npt bushing. I added sealant to the threads and then screwed in a 1/4npt (w/sealant) with a barb fitting. The existing overflow hose was cut to length and then I added an overflow hose to the upper portion of the tank. I used the existing horn mounting bolt so no holes were added to the inner fender. I will add coolant in the tank tomorrow and test drive it for leaks.

Thanks for the replies!!