Do you need the 'specs' on the Head Bolt Length.
First check the threads closely, and make sure there is no
progressive wear, and/or corrosion.
Thread size is 7/16"-14.
You can purchase a 'machined nut', and run them on the
threads of each Head Bolt to check to see if there is any excessive play.
That is the 'least expensive way' for a quick check.