I have seen two cams and or timing sets in the last two weeks that had the cams retarded 13 degrees in both motors There is no way I would change one part of the valve train drive or cam on a existing motor and not verify the cam lobe centers on the new cam or timing set, even if just changing the chain As far as changing the valve springs on the heads on the motor it depends if you have a stock rocker arm set up or the after market set up like bolt on Jesels or some other brand If stock I think LSM has a tool to use BTW, do you have a way of checking the valve spring pressures now and do you have a spec. on them when installed new? If not you may be shooting yourself in the foot by changing them