You have the wrong pivot! (Which is why you're having problems finding the right coil.)
That's a very rare 68 427/390 only pivot and I know several guys that would love to have it!! As a matter of fact, I just contacted a guy on the NCRS looking for one, so you might be getting an email. He has the one YOU need!
My picture above is what you SHOULD have, and here's a page from the Chassis Service Manual showing what you DO have (far right drawing).