here's the pics from my afternoon yesterday. spent 2 months asking around for the "proper tool" or a recommendation for a shop when I should have done this from the beginning. took me a couple hours to make it up and test both sides.
The only problem with using the heads for pressure testing is that you can't tell where the cracks are as well as you can with plates if properly made. If a person doesn't want to pin the leaky cracks then it won't matter much. Some cracks are in places that can't be pinned anyway like the ones down inside the center exhaust port area. If it's in the valve pocket and doesn't go too far down into the bowl, it can be pinned. Most exhaust valve seat area cracks can be seen with the naked eye so that's the first place I check.