Serial number location and why does the parts catalog nor recognize the one I have

I have a 2001 Chapparal 280, with twin 4.3's The s/n's on the registration start with M05####, both of them, I will check the actual tag when I go to the marina, but I have seen a picture of the tag on the Stbd side near the block and flywheel cover. When I enter the S/N in the search for parts, it doesnt come up with any matches. if I search by year and engine size, the S/N's start with a bunch of different letters none of them M like mine. any suggestions on how I can find out exactly which 4.3, V6's I have? and it doesnt look like a 2 barrel, but a 1. I will double check,

Thanks,
Oxnut23 I have a 230C Sea Ox as well!

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