That is so correct. I actually did that on my 69 Roadrunner in the middle of winter. My freeze plug on the back of the head was leaking. I judged where it was and drove a screw driver through the firewall. Opened it up enough to replace the plug. Sealed the hole. Hay in 1973 I did not have a job or money to fix it correctly. Thanks for jogging my memory.Just for kicks , do the holes happen to line up with the freeze plug in back of the head? If so thats the way line mechanics replaced them. Saving the customer $s and saving you from having to pull the heads.