Dave M. ran a 26p B1 when his boat had a 385HP/454MagMPI. and I ran a lab finished 26p B1 with a modified 340?HP/7.4MPI.
Both Dave and I run 28p B1s now...
A stock 454mag makes max power at 5000rpm so that is what you want to prop for...

Razor, figure out if you have a Gen V or Gen VI engine. Bulding 50HP more is pretty straight forward.
If you have a Gen V then use the Merc/Crane 420,425,525sc cam. This cam is what most guys use when building up Gen IV and Gen V low output 454s.
If you have a Gen VI engine then I would consider using the ZZ502 crate motor cam. After-market roller cams and lifters are big $$, but the GM stuff is not.
You will need to replace the valve springs to match the new cam, and the non-adjust rockers with an adjustable setup.
If you decide to have a valve job done, have the heads milled at least 0.010 to boost the compression a little.
And like we've talk before, you will need a double pumper carb and ignition changes.
Have fun with it...

Mine is a Gen V, non roller cam. I will take a look at the Crane cams. Is a Demon carb worth the money? Will it bolt up to my intake manifold (do they make an adapter)? When it is time to do the shortblock, I may make the change to the 502. I just want to make sure everything I look at is good for the switch.

Since, you have a Gen V, a full roller cam setup does get costly. I'd stay with a hydraulic flat tappit cam and add roller rockers...
I work with a fellow that bought a Demon for his car and loves it; he said it was much easier to setup than a Holley. Personally I have no experience with them.
I believe that your GM/Merc intake will except both bolt patterns and does not require an "adapter". It does require a spacer to cover the larger secondary openings meant for a spread bore carb. I think you have a 4 hole spacer under your Carter square bore carb now; if not, you should.
You could just re-jet your 750 Carter to try with the bigger cam. Merc used the same carb and intake on the 390HP/502. The only difference was the jetting and an open spacer. A 750 carb is good to about 5200rpm on a 454.
If you do decide to buy a new carb, my first thought is to buy the same Holley 800cfm carb that Merc Racing used on the HP500/502. Lots of places sell them so you can get a good deal. The Sea Demon comes 750 or 850, so if your thinking bigger cubes down the road, 850...

Superbabi,yes that is where the harborside is,a nice clean place,i'll be goin back next year,are you?? tripps

Tripps, what one were you in ???

Razor your boating expences have just started. better get use to it. every year you will be adding more stuff. Superbabi had a quize a while back . What does B.O.A.T. stand for ?

"Bring On Another Thousand"
or "Break Out Another Thousand"
or was it "Break Out Another Ten thousand"...

Razor, full force boating will..................SUCK YOU DRY !!!!!!.............Ahhhhhhhhhhh gotta love it.

Super,the one that is facing the Atlantis by the dock. You can get basicly anyone you want,book on a saturday arival and you get a view of the pool,so you can watch the kids in the pool as you sip Kiliks from the baloncy tripps