How does one go about verifying engine hours on a set of 1999 500HP's (EFI)? Doesn't the computer chip store hours? What do you need to "read" this info?

Thanks!

The Mercury DDT, any merc dealer should have one.

Hours "follow" the ECU.
If the ECU's have been replaced or swapped with a low hour ECU, then the reading won't tell you squat.

If you have reason to question the reading then you should do a full leakdown to assess the condition of the rings and valves. And a 500EFI can be in need of valvesprings in as little as 100 "spirited" hours and lifters in as few as 150 hours (easier running can extend those to 220/300 hours)

What should I expect to pay to have a leakdown test done on a twin engine boat?

Thanks for the help!