Well...that's the rub. He's not explained WHY he thinks this is so, other than a random "but the longblock, upon inspection, is not a Mercury Racing product"
No way he'll ever prove anything, more than likely. Now the onus is on HIM if he ever wants to sell it and have full disclosure...so I guess that is...that. One wonders how this would ever play out in court? Let's say he's called a dozen experts and the engine is torn down to it's basic components, and they all swear that no indeed, that is not Merc Racing parts...what's to prevent the dude who sold the boat saying, "Hey! You switched them out!"
?

True story. So whats the numbers on the block? Also sometimes sh it happens and you get screwed. Doesn't make it any better but it happens. I had a conflict I had gotten in with the city that I have my business in. Words were exchanged and the who has the biggest Richard started. I called my attorney and he told me this. You can pay me and you may win or you may not. Its all up to a judge and if he or she is in a good mood or not. Im going to charge you as much if not more then what the city is wanting you to change to be compliant. Long story short is sometimes your better off not splitting hairs and bite the bullet and take care of the situation at hand and move on. Thats easier said for some then others. Sometimes you have to take the emotions out of it and treat it like a business. Whats the easiest most cost effective route to go?!?!

Lawyers cost far more than forged cranks and rods. Unless you’re just feeling vindictive, or you’re a lawyer.

Or your Ex's brother was once married to a girl who's new husband is a lawyer, and he said you have a slam dunk case and you will get punitive damages in the millions....

The 500 efi is not a 525 efi and any comparisons will be invalid.

I don't think any info from an online forum is going to be of much help.

You presenting info like, "Hugh G. Rection on OSO.com says I need to pull my crank to see if my rod is stiffer than everyone else's." would be funny, but not going to gain you anything.

In all seriousness, you're asking about an engine that is prob close to 20 years old (unless it was advertised as NEW. In which case, the only info that is worth anything is going to have to come from Mercury Racing directly. Something along the lines of my engine, serial # blah, blah, blah was assembled with such and such parts per VIN code etc.). that SHOULD have been serviced by what, 200 hours? So at that point, someone had to replace gaskets at the least. Who knows what else? And seeing the Teague flame arrestor says it's been altered from it's original design already, I think you fall under the buyer beware category.

I am making a joke, but at the same time, without knowing the specifics of the case, think you have a very uphill battle ahead of you..

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The serial # should tell you what they started life as.
https://cimg9.ibsrv.net/gimg/www.off...832a0cb3f6.jpg

First generation 500efis had GM dimple rods. Later generation had Manley rods.

A 502 mag short block and early generation 500 efi have the same internals. Pistons, rings, crank, rods, block, hardware etc. only difference was who assembled it. Then the heads cam lifters etc all too end is different.

Theres different variations of 500 efis, I have rebuilt "early ones", they used the same 1053 steel crank, rods, pistons, rings, windage tray, oil pan, harmonic balancer, timing chain, gen 6 block etc. The heads had 1 piece manley inconel valves vs two piece a 502 mag uses, 7/16 studs vs the non adjustable smaller threads a mag used, crane gold rockers vs stamped steel, a 731 crane cam vs a low performance cam. later ones used better rods that were full floating