Your OEM heads have a valve guide seal to retainer clearance that limits camshafts with .444" intake and about .452" exhaust. The factory 340 cam was ground with mild lift numbers for this reason. To install a larger camshaft lift you will need +.050" valve keepers. For instance, installing a camshaft with .480" lift will likely defile your valve seal do to limited clearance. Your multi-grove keepers are the other issue at hand. They may not be available in +.050. Therefore you will need some crower +.050 spring retainers, or have a machinist knock the guides down -.050" not recommended. That's the reason most Mopar cams are Low lift long duration, until you get into aftermarket valvetrains.
