These are all sold under mercury REMANUFACTURING division so emissions do not apply

The 454 will have more torque and prop turning ability at cruise speeds. Although the 383 may make more horsepower, it would be up top which sounds like not what you want. Go for a 502. Add a 100 horse and that much torque.

If going up in engine size would boring my 454 to a 496 be a better option?

You can bore and pull more ponies out of it, but going full out with a new crank is do-able, but I would just go for the 502. IMO it would cost lest and drop in and go

There's a pair of 496's in the classified with 117 hours for $9500 each.

I am going through the same decision process right now. Replacing a 454 on a 24' pilot house that weights 7000lbs loaded.

The 383 sounded appealing, but I believe the loss of torque at low end would offset any efficiency. So for me, it is a no...

A lot of people are hot on the 502, but I do not see how it would be any more efficient, and might even cause outdrive failure problems from the increase torque and HP, depending on your drive. for me...it is a no

So after coming full circle, I was down to the 454HO (385HP) and the base 454, or a Vortec 454. The HO model will have power at the upper end, where I hardly go, so it is out now as well. Sad about it, because I love the internals. Even thought of buying it, and swapping off the heads for oval port ones, and a torque focused cam. But then, I am looking at a total of $8000. not bad, but much more than the base 454.

The base 454 or vortec is the easiest swap. They will be the most fuel efficient. At $3800 for a rebuilt, it is 1/2 the price of the HO. For you, I would add in the closed cooling system, and run for 2-3000 hours if you care for it.

I bet the 385 horse mag makes more torque everywhere over the base 7.4