Ausdok; The thickness of compression plates is usually determined by measuring the clearance between the piston and cylinder head at TDC. Known as the "Bumping Clearance" it is measured by placing a piece of led on the piston and measuring its thickness after the engine is turned over TDC. My instruction book for the HD9 engine make no reference to to this adjustment. Does your engine have any shims fitted. If not I suspect these engines may have been built to a tolerance that did not require adjustment by using shims.
Hugh