Got in some parts from AMK (who are outstanding by the way).
So I've settled on #8 phillips pan head screws for now. Although I think #8 hex head are the proper pieces (5/16" head) they still make it hard to get a socket on them. Obviously the phillips don't have that issue.
In another twist .... the misalignment I'm seeing is probably due to the fact I apparently have two different turn signal lenses. Both are SAE 68, one is Guide 23, the other is Guide 25. On has a capital "T", the other has a capital "P" .. which I assume is Tempest and Pontiac. They are NOT exactly the same, the holes to access the housing mounting screws are in slightly different places ... I'm thinking this is the cause of my problems, and why one side fits better than the other.
Anyone know which one is correct? One has "pebbles" on the inside, the other has them on the outside (yes I never noticed this before).