Well I went to install some NGK BR8ES spark plugs and realized half way through that the head is way too big to tighten down. Looks like the head is 13/16 and I’d assume the LS heads can only take 5/8 head spark plugs? Is there anything that’s equivalent to that plug in a 5/8 size ?

 

The equivalent in a NGK BR8ES that would fit LS heads I believe is 1049.