I ran into an issue that required these plates be built, and it really helps out.
Here is some background.... 15 years ago, Bill Jones showed me what I feel is the best way to index a cylinder head when flowtesting. He liked to use two custom dowels in head bolt holes to locate the head on the perch. The theory here is when flowtesting heads your procedure must be quick without sacrificing accuracy. The head can be unclamped, taken to the head porting station and back on the flowbench very quickly.
With this system, you gain time as you are not unbolting from a sliding plate and you gain accuracy because these dowels will reposition the cylinder head on the perch very accurately.
I have used this technique since Bill opened my eyes to it, and because I have tested a wide range of cylinder head types, I need alot of indexing holes. That means I ran out of real estate for the bolt hole locations. So this plate was developed so that my perches could have all the different patterns, but without the hole location overlapping. Typically 3 patterns can be put into one plate, maybe more. It depends on which head you are going to test.
These plates are .125 thick and with the wide range of head perches out there, these can be sized to your perch deck, and bore size. You can choose from the following bolt patterns:
Chrysler Small Block
Chrysler Big Block / HEMI
and others if you provide the blueprint dimensions
Your perch must have the common 5" square bolt pattern to position this index plate.