Mercruiser Identification

"I bought a '69 Cruisers w

"I bought a '69 Cruisers with what is supposed to be a Mercruiser 160 engine. I picked it up without listening to it run because I was looking for a project boat and for the price I paid for it, even if I had to put a grand or two in it, I would have a nice boat.
Here's the situation: The engine was rebuilt 3-4 years ago. I pulled the engine to replace the gaskets and to check it over.
The manual that came with the boat has an engine serial number of 2562505 handwritten in it. While looking at the manual a little closer, I don't see the bolts that fastens the manifold to the block in one of the pictures. Mine has has long bolts that runs completely through the manifold into the block and the illustration in the manual shows a *smooth* casting surface (I'm unsure on how it bolts on).
I then looked for the tag on the engine block flange to check the serial number, but it wasn't there. Also the engine is painted red instead of black. The decal on the rocker cover is missing too.
So now I am wondering if this is something other than a 160 or if the engine block is not a marine engine, but out of a GM truck??
Any ideas? Need to decide which way to go from here.
Thanks in advance folks!!"

"I have the same problem. GM c

"I have the same problem. GM casting numbers from my block show that the engine was made the year my boat was built. After checking around; with out a clear answer from anyone, I figure that the block is the same as well as the head. The difference is the crankshaft and the cam as well as the fuel pump/carb. The starter and alternator are also different, but the cam and crank are the most important as the other stuff is readily available. The cranks are more durable for the marine application and the cam is a different lift and duration. I got a used marine cam for mine for $50 and I am still looking for a crank. This is what I have been able to figure out from all the posting that I have done on the net.
Hope this helps."

"rotaxtwin, when I asked a mar

"rotaxtwin, when I asked a marine mechanic about the difference between the truck engine and marine engine, he didn't mention the crank, carb, or fuel pump being different. Hmmmm??
The casting numbers on my engine is the same year as my boat too. I need to dig a little farther.
I'm kinda' interested in finding out how you make out with your engine. Good luck!"