John...I've seen similar questions by different posters that have been asked on this board before, not necessarily mine fwiw...and it's amazing the difference in responses given depending on who posted the question. Is what it is.

I completely understand the "correct" way, is to measure it and again I understand the catastrophic consequences if I get it wrong.

Currently running the MP557...no idea on where I'm at, again don't have the tools to check it. Been running now 2 years...a friend has offered a nib 590 he's never ran, thought maybe I would give it a shot. Cam has been around what 30+ years, and I'm guessing someone at one time has tried running it in a zero deck motor, if it worked with a old TRW 6 pak piston, I would think it should be ok with mine...might be I'm wrong, don't know.

I've actually met Mike in the pits a few years back, seemed like a nice enough guy...my apologies to him for being so curt...