I am trying to do a leak down test on my 97 GT. I have a OTC leak down tester that I can't get it to screw into the heads. It screws into a set of 09 crown vic heads I have but not the 97 heads. I assume it is because of the spark plug thread count. The plan is to replace the 97 heads with the 09 heads but I want to do a leak down test first to verify the rings are OK. Any adapters available to make this work?