Im useing a used cam now in my 512 but I did get it from a friend so I knew it was good.One time in a small block chevy I put a used solid lift cam in but did not have lifter I had a set used big block lifters spent a little time on a surface plate with some wet/dry and lapped them in a figure 8 pattern and ran it for six years untill a connecting rod broke and shattered cam I agree with above post saves the worry of breaking in a new cam if you know its good.