318 expansion plug leaking

Can you sneak say a 3/8 rod in there between the pipes? Doorman used to make a tool I could loan you since I have one.

I have the headers all wrapped up. Wont be able to get anything through there. Either way the header will have to be removed. The space is really tight. Just would like to know if anyone has had luck with installing in car. The expandable plug is an option for now. Im getting married this September and this it's our wedding car.