That's a 365HP Mag motor. The 420 had Gil exhaust, different intake, etc.

420HP also has a holley carb

Yes. This is my concern as well. From the picture above, do you think I'll likely be able to see the engine code stamped on the back? I'm doubtful even with my camera phone and mirror.

http://www.marinemechanic.com/merc/d...lockcodes1.PDF

sorry about the multiple posts. was getting an error message.

The 370HP, was part of the cyclone "high performance"series of engines. 370, 400, 440, 460, all had the crane golds I believe, except some of the early 370s. They also had the finned valve covers, and a couple other goodies. The 365 Mag, was more of a run of the mill setup, produced more as a production line engine from mercruiser, for the bravo boats. The first "365" mag, came out in 1988, with the bravo drive. The 365, and 370 shared the GM cams, and mostly everything else. The 400HP and up, had bigger cams from aftermarket. .

Yep. 365hp@ crank and rated 350hp at prop.

So what do you think of 500 hrs on it if oil changed every 80 hrs? Apparently he installed it at about 350 hrs and put 150 hrs on it. He and a buddy did all the work so he has no documentation. Doesn't inspire confidence. It is driving a freshly rebuilt Bravo 3 thought.

Anything in particular I should look for?

A stock , well maintained, 365HP mag engine, will go 1000 hours. There's no guarantees with buying a used boat, used engine, etc. All you can do, is do some basic checks, hope for the best, and expect the worst.

SB,
You are not wrong. In the late 80's the Mercury 454 420 HP came with cast iron manifolds. As many failed and leaked, Mercury recalled and replaced the cast iron 420 manifolds with Gil exhaust. The 420 HP package also came with the heavier duty Green Tag transmissions vs. the Red Tag trans on the 370 HP.
Ben

1st off, is the boat a good deal? How much is he asking? It is a 1979 and unless it has been on the trailer it might have a wet transom. Does his story jive about the engine swap? Where did the engine come from? What kind of bot did it come out of? How does the installation look? Do all the wires going to the engine look professional? What kind of 233 is this? A 233 from back then would have had a TRS drive if it was a BBC or a MR if it was a SBC. Questions I would ask would be:
1. did you replace the bellows
2. did you replace the gimble bearing
3. did you replace the shift cable?
4. did you replace the water pump impeller?