Another update...

We took apart some of the head today. Got the cams loose, pulled the lifters at cylinder 3 and 4. Tested those and checked the springs...

...and unfortunately all of them look good.

Looks like we have a burnt valve or something worse.

Next plan of action is to pull the head off my parts can and have it completely rebuilt. Then we're going to swap the head out with the old one and do the head gasket (obviously). In theory, this should fix any problem that we have.

And if it doesn't then I'm going to cry.