Vacuum on 1968 GTS 340 4 spd.

Ahah.... that would do it! Not the first error in a compression tester. My 40 year old NAPA tester keeps giving good results so 'knock on wood'....

BTW, you mentioned a 8 to 10 in vacuum increase... was this with the right side shimmed up or ???

As for cartoon characters.... this reminds me Joe Btfsplk, the world's worst jinx, from Little Abner.. that was the guy who walked around with the rain cloud over his head all the time... LOL
Btfsplk