The 4 barrel carb motors are mostly rated 260 horse til around 1994 when they started calling them 250. I think that happened with the Weber carburetors.
I was looking in the engine ID list just now where there are some 1994 #s used in 1995, so don't be surprised if there are some conflicts. They rate the 2 barrel 235 horse in that list. And they call the 250 HP a Magnum, where Magnums in some earlier years are roller cam 300 horse 4 barrel and fuel injected engines.
All of these are GM 5.7's. So it's tough to get it all straight.
Here's a link to the chart
http://www.4shared.com/web/preview/pdf/TcRI4n4z, it's in the stickies at the top of the Mercruiser forum. Look around page 41 & 42 and you will see what I am talking about.
Chevrolet Performance rates those same engines based on what heads they have, and can be 275 or 300 hp if the 64cc combustion chambers are in the heads. You won't find that in the Mercruiser stuff, but it can be found online. To check that factor you need to remove the valve covers and get the head identification #s.
I think Mercruiser is rated a little lower because they are more conservative with the timing.
