273 rocker arm clearance

What I have is a Hughes Engine rocker shaft and shim kit with modified 273 rockers. The rocker arm shaft comes with aftermarket clamps thus the stock dimension between rockers is lost. Have installed shims as to maintain center on valve stem. Does anyone have any knowledge as to what the stock clearance was between rockers or by experience what this might be. It can be expressed as between individual rockers and or clamps or as a total dimension just between clamps with rockers moved to one side. Hope my last statement is understood. If I had the hardware for the 273, I could do this but I don't. Thanks for any response. Jeff