My 2 cents... In post #10 the return spring bracket seems to be mounted in the wrong place (on top of the riser rather than one bolt farther back where its left side would fit into the pocket in the manifold.)
If the return spring bracket was mounted one hole farther back that would leave the riser bolt hole a perfect place to mount the ground cable.
FYI the 65-66 273 in its OE red in the garage does not have the front head bolt drilled like my 67 does.