Tim,

I think I have that same plug and pay it no heed.

added later:
I was wrong, Tim, I do not see that plug in this photo?

I think the 1959 261 in my old truck had that plug, however. Maybe someone who knows about that plug will reply.

Last edited by tclederman; 12/24/2012 3:38 PM. Reason: added 261 block photo