Thinking more about your "flathead-and-a-half", I wouldn't do anything before making sure I had a clean set of plugs in place to see if the problem lay there.
I never was around the v 12 much but my experience with the same tech v 8 ford made me believe that they were much less able to deal with plug fouling conditions than our chevy 6.The chevy would live long and work well with high oil consumption that would foul plugs regularly on the Ford flathead.
And now we have problems finding the right heat range plugs for the old flatheads (18MM) and our fuel likes to short a coated insulator more than usual--this adds up to my suggestion to look to the plugs first for this trouble.
Good luck and keep us posted please--we're learning too.
