My 59 235 has the slinger. The keyway in the slinger is to be able to slide it on over the damper key without having to remove the damper key. I have an aftermarket timing cover that I had to elongate the mounting holes a little because they put the seal out of line with the damper pulley. I threaded my crankshaft and honed my pulley so it can be removed more easily. I installed the seal in the cover, installed the pulley, then checked the timing cover holes and made the correction to the cover. That way it is perfectly aligned with the seal/crankshaft pulley. No leaks.
