Engineer & Zip, definitely not wrong about the springs, but the next question will be why the roller lifters went bad so quickly and wiped out the lobe on the camshaft.
EJ48315: Just because the springs that the tech guy sold you physically fit, doesn't mean that they are the correct ones for the application and will not cause you other problems. It is not all about higher RPM's, as the ramps on the solid roller lifter camshaft are steeper than the ones on the hydraulic camshaft. This causes the valve to be thrown off of the seat and with your heavier valves it causes the roller lifter to not stay in contact with the camshaft when it goes to close the valve. This causes the roller lifter to bounce on the cam lobe and will damage the roller bearings in a very short time and will in turn cause the roller lifter to fail which will then wipe the lobe on your camshaft. Something else that you might try, that is not used very much anymore because the valve spring technology has gotten so much better, is a rev kit. The rev kit installs on top of the roller lifters to the bottom of the heads. This will be extra spring pressure on the roller lifters and will keep them planted on the camshaft.
Just a thought,
Bill Mitchell