1-1/2" - it's one of the six plugs that go into the block, three on each bank. Look up 302 Windsor plug kit on ebay.
Still a work in progress.
Still a work in progress. The tank is being modded by a panel guy I know, will post pics when it comes back.
Aesthetics... I don't want to hide the rear valve bank, I want it to be obvious that the bike is a V4... I also think keeping that bit open "adds lightness" visually: