340 with 302 cast head for pickup

302' heads come from the factory with 1.78/1.50" valves.....and 318 spec light duty (wimpy) springs.

If guides are standard height..(not machined)...then Valve retainer to Valve seal clearance is still the same...around .490-.500

But you mention slightly stiffer springs....

I personally would recommend/use some 587' castings....or 915-J's....with 1.88/1.60" valves as a Minimum....if not 2.02/1.60 valves.....that have .550" single springs with dampners, and that have the tops of the valve guides machined down and race type valve seals installed....and eliminate the rotators from the exhaust valves....and let you slip just about any cam you would want in there...under .600" lift.

318 heads...although they WILL fit....are not Optimum in any situation...for a 340.

:farao: