"Anyway it turned out that even though the engine timing was 5 degrees atdc @ 750 rpm , per book, the timing was too retarded. The ticking went away after advancing the timing to 15 degrees atdc."
Don't you mean 15 degrees BTDC? If so that seems to far advanced. Did you unplug the vacum retard? I think it shoud stay connected when you are setting the timing. My 72 sl runs best at TDC or 5 BTDC when I am running premo.
Anyway is your 72 like mine with vinyl interior, roll up windows?