FWIW...I got a real education on this stuff after talking with just about every supplier out there...from Specter, MAF, Downey, Marks Off Road, Wemberly in TX to proffits, to Rcky mtn cruisers and classic cruisers.
I ended up just ordering one from Narkek for about $85US shipped. It arrived yesterday. THANKS WES~!
Here's the jist of what I learned from all this. Pretty much no one replaces the vac advance b/c they are all but ubobtanium here in the states. so here's what options I learned about...option 1. do the FJ60 dizzy swap with the side cover. option 2. go HEI 3. Have all the Cruiser suppliers laugh at you asking for a vac advance for a 77. 4. get the rebuilt older style full vac advance dist. from Marks off-road with the adjustable vac to compensate for octane - everyone said that'd work fine, too. about $225ish?
so...notice replacing the vac advance wasn't in there?
well, I had already purchased the pertronix for that dizzy - the other options were more expensive for sure. Nardek had lightning fast response and shipping turnaround (keep in mind they're in AUS).
Hope that helps a fellow 77 owner...there were more details about vac retard vs. vac advance and what years they switched from one the other and back again. I Bet Jeff Zepp knows all those cutoffs by heart, I'd have to look at my notes. Interesting stuff for sure.