Hey Pat,

A leak down tester is used on GA piston engine stuff during inspections. We also used to use one on a buddies NHRA car for tracking purposes. On full scale piston aircraft engines used in General Aviation, an input pressure of 80 psi. through a metered orifice is supplied to the cylinder with the piston at TDC and the residual pressure is measured on the second gauge. Generally a loss of 20% is considered as the maximum allowable before finding and repairing the cause of the leak, usually exhaust valves on GA stuff.

They use a standard air chuck fitting screwed into a sparkplug adapter, so the difficulty would be in obtaining or building those adapters for the sizes you need.