A machine shop can make it a 4 bolt main, problem is they probably used cast internals. Large ovals will work best for what you are doing so you are fine there. Good luck with your mistery engine. Let us know what you find out.

The "PASS" stamped into the heads means they are the small peanut port heads. The 365HP magnums had the big rect port heads, which were stamped "PERF" in the head. Someone probably blew the 365HP up, and replaced it with a older 454/330, or possibly even a 454 out of a car.

Im not sure, but i thought the truck 454's from GM, had cast internals and peanut port heads, but 4 bolt mains? Where as the car 454's had 2 bolt mains. Not too sure on that though.

I believe these are the large oval heads. I have seen the peanut ports which have very small intake ports, with lots of material between the ports. These are very large intake ports that are basically rectangular in shape, with rounded corners. There is very little material between intake ports, they really couldn't be any larger. Would the casting numbers tell me what they are (besides year)? Does anyone have pics of the difference between peanut ports and large oval?

The old 2 bolt blocks from Corvettes and Camaros etc said Hi Perf Pass on them. Not unusual. By 1990 Chevy was using the Vortech heads on 454's. You can i.d. them by the sharp point in the combustion chamber between the valves. This engine sounds older with the newer tin on it.

My 454 Magnum Alpha is an 87' and it has 2-bolt mains.

454/330's were a "mixed bag" of 4 bolt and 2 bolt blocks. You could get either one. Internals were cast. The early Mag might also be a 2 bolt, but the later Bravo ones were almost all 4 bolts. All Mag/Bravos were forged internals. All Mag/Bravos were rect port heads and aluminum dual plane intake.

454 365 hp magnum question
 

I'm new to boatingand looking at buying a 1990 formula with a 454 magnum 365 hp. How can I make sure its a real 365 hp not a 330 hp with a flame arrestor cover that says magnum on it.

Yes. Pull the valve covers and post up the head casting numbers. Last digits being 781 or 049 were common large oval port heads.

Here's a pic showing the difference.

http://www.cartechbooks.com/cartech//SA48/5318.gif

My old 1990 330hp Merc has peanut port heads and they are stamped "TRUCK" and the block is a 2 bolt which is stamped "HI PERF PASS" it is for sale in the swap shop I don't think the pictures in the post show the stamps but I could take better pictures and send them to so you can compare to your engine. Send me a PM if you want.