If heads are in good shape you may be able to find a take-out HP500 cam for a nice power upgrade. An HP500 EFI cam would probably be safer to run than the carb version - the wider LSA is less likely to cause reversion. Caution - going to any performance hyd roller cam will almost certainly mean an exhaust upgrade too. If you just want to get it running again and don't want to spend the money on upgraded exhaust, stay at less than 225* / 230* @ .050 and keep the LSA at 114* or greater.

You may want to keep your eyes open for a set of the Merc manifolds from the LS-series 496 engines. They are lighter, and they eliminate the problematic wet riser joint that has killed many an engine. They also flow a little bit better. You should be able to find a set of take-offs for $500 - $700.

I would stay with the 454 on a boat that size. I built mine into a 489, and it is indeed a slippery financial slope when you cross that threshold. You will find yourself dropping thousands on cam, valvetrain, heads, exhaust, intake, carb... the list goes on and on.

If you have full time thru hull with '80's y pipe delete you might be able to get a rumpity rump.741 roller style cam and get a gil exhaust and risers for price of stroker crank kit and all be careful with water flow and dump plumbing it will have some nice rumble at idle and you will feel the extra 50. -60 hp when you hammer it let's see the tear down pics

repeat my question from post 9. salt water or fresh water? the heads can look really good and have good compression and have rotted out at the exhaust guides and pass water. if block will clean up with overbore ok. if it needs sleeved i would consider replacing it with one that spent it's life with antifreeze in it. if you need exhaust anyway cuz they are old and suspect, it is hard to justify buying stock mercs again. get the heads pressure tested.

It has always been in fresh water. Idk if you saw it but it has like 315 original hours on it. The exhaust it straight out the back no y pipe or anything. Idk if I can justify spending 2 grand on just an exhaust.

no point in doing engine improvments if you are planning to keep the stock iron exhaust manifolds. that would be my first mod on a 454 mag

Lots of gil manifolds sets out there . Think your going to have to step over to the land of divided exhaust runners ,or forced induction if you want 400+

What are some good exhausts that aren't 3 grand? I was looking at rewarder custom headers. Are they any good? I could spend maybe 1500 on an exhaust.

Ok guys I need some opinions here. Thought about it and I don't think I'm going to stroke it. If the one cyl is scored maybe I'll bore it 30 over and possibly keep the original forged crank and connecting rods. Now for pistons I'll get some forged ones but what compression would be good. Also what about a mild cam, intake manifold and carb? What would be a good set up and possibly some exhaust mods. I don't have a million dollars to spend on the engine. I just want some honest opinions.

FWIW a long rod 454 .030 over is a great package and it work with your stock GM forged crank, you will have to change pistons and rods. great torque

dana marine is less or about 2000. They make numbers equal to CMI E-Tops