You would need to know the name of the cam manufacturer, and probably a cam part number, and contact them directly- - - -assuming they're still in business. A "3/4 cam" stands for "3/4 race"- - - -a grind that's almost, but not quite designed for all-out competition. Those cams were called "Full Race" back in the dark ages when the cam specifications were carved on stone tablets for Julius Caesar's racing chariot drivers. These days, cams are usually classified by degrees of duration, with a slightly more radical than stock item having around 270-280 degrees of valve open time, and more radical ones in the 300 degree range or more.
Here's a shade tree method of finding a good clearance specification- - - - -with the engine fully warmed up, set the clearance to the penciled-in numbers on the door frame. If the valves are noisy, start reducing the clearance a thousandth or two at a time until the noise is at a minimum. Exhaust valves generally need a couple of thousandths more clearance than intakes, because the stem length "grows" when exposed to the heat of the exhaust gas on a long uphill pull.
Jerry
