I like the Valve spring tool from Mancini , use air pressure or nylon rope in the cylinder to hold the valve closed & bolt the tool to the rocker pedestals & it levers down on the top of the retainer , easy to use . With a dial indicator you can measure the cam lift & maybe determine what cam you have , I would use a slightly overkill spring than something marginal for spring pressure , Lunati cams have a fast ramp & require more pressure even for the same lift to keep the valve train stable , it is possible that the spring hit a harmonic or could not keep the valve train tight & bounced causing the failure .