Hey all. I have an opportunity to pick up a stock merc hp500 long block with je pistons and afr heads, for roughly the same price as what it's gonna cost to build my 89 454 mag to 500hp. It's a new block with no run time. I'm curious if all my accessories, flywheel, bell housing, cooling system, oil pan, sensors, wiring, etc would transfer over? Do these need additional oil cooling vs a stock cooling log? I also have a cooling crossover tube ide like to use as well. I just picked up some gil manifolds im using on whatever build I just need the right risers.

Those AFR heads will probably have a .300 raised exhaust ports so pipe alignment might be an issue.....internal external balancing might be an issue also

What do you mean by balance? Also I have no idea how my pipes fit yet as I haven't pick out risers.

Some engines are internal balanced which are neutral on the flywheel and balancer and others are external which have counter weights, you cant mix them

aren't both of those engines internal balanced? I know my crank had dimples drilled in it. The hp500 has the stock merc crank and rods

you,r 98 454 is a gen 6 externally balanced engine,you need a flywheel from a gen 6 but a gen 5 might be the same,do you know the year of the hp500?all big block 454 and 502 engines from 98 on are gen 6.hope this helps.

I will have to ask what year the rotating assembly Is from. Mine was an 89. I'm sure a flywheel isn't that expensive if I need one? Are the rear mains both 2 piece? Oh not so my oil pan won't work?

The Gen V and VI have the 1 piece rear main seal. They shar the flywheel pattern and are both external balance from the factory. You can find nodular iron flywheels reasonably.

You oil pans from the Mark IV will not fit.

But Gen VI blocks have factory roller cams...a step up from running FT.

I would be inclined to go with the HP500 and AFR heads.

Does the '89 have forged internals? Mayne some value to sell off there? Offset the oil pan and flywheel costs.

yea forged internals 7/16dimple rods 4 bolt block. It's all at the machine shop now getting evaluated. But my almunium heads are rough and I need a full cam and valvetrain. I like that the hp500 is basically stock at the end of the day. I can get the gold comp rockers. My next thought is the block shows a fuel pump hole but does a stock hp cam support it?

Most GM 1pc rear main blocks don't have the fuel pump casting. Gen V was totally removed. Gen VI was cast in for some models. Aftermarket blocks will vary.

The Gen VI roller cams likely have the fuel pump drive lobe.

Performance stock design for marine is a large benefit. Easy on cams and valvetrain.
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At the end of both equations, with X dollars spent being equal, (as you mentioned) with the HP 500 you'll have a better modern engine with reliable 500hp+, and the mark IV forged parts to sell.

Running FT cams is getting harder every year. New parts of course. Even sourcing good aftermarket performance rollers is becoming difficult.