Mully with your cam your spring # is 279# not the 339#.The 339 is if you compress the spring fully so you are fine .I just ck the specs for the 942 springs 115# at 1.700 ht and 284# at 1.200 you are at 1.226 at 279#.i hope this all makes sence .As for 500# of pressure I would not run any cc rockers .I have read about far too many burn up and lockon the shaft.Remember the motor challenge in mopar muscle Diamond race engines got knocked out because of this.