I remember NHRA using 125 lbs. on the installed height and 300 lbs at .500 lift when I use to race my 1963 415 HP M.W. stocker before NHRA did away with using the stock factory spring loads specs.in their tear downs It was the same spec on both M.W. motors in 1963, not the same in 1964. I'm not sure about the 1962 M.W. specs. either
On any solid lifter cam motor I build now I set the valve springs up on I use from 140 to 160 lbs. on the seats and from 325 to 375 Lbs. opened at what ever the max lift at the valves are minus the lash Make sure you have between .060 to .100 clearances between coil bind and the valve seals to the keepers or retainers, which ever one is the closest also