Thanks!! I spent about 2 hours doing searches but couldn't find it.
I thought of that. When I was a teen, we used those. I was afraid though that they might not be as accurate. I was able to get the adapter though thanks to the guys that posted earlier.Why not gut an old plug and weld on an O2 sensor bung?
Another option is to use an old-style hand-held compression tester - the ones with the big rubber tapered end.