Vortec 5.7 Engine & Head Numbers

Hi Guys
I Bought a brand new ski boat with a Brand new 5.7 Vortec.
( or should i say I ordered & Paid for a brand new engine ).
after about 3 hours of running in it developed a miss. turned out to be
a broken valve. I know this can happen on a new engine but a few little things make me wonder if it is just a reco'ed one.
Has some black paint overspray on the sparkplugs and has developed some
surface rust on the block.
Can anyone provide me with a list of engine number prefix's or block numbers
etc. so I can check that I have got what i have paid for.?

Thanks for your help & time in advance.
Adrian ( Australia ):banghead: