Quit over thinking it, just do what Bob recomends. He is the cam guru. Just get him the information he needs and tell him your goals.

You probably only need 500-550hp to exceed you goals.
So.....do you build a good breathing 496/502 that makes 550-600hp or do you strangle a 540 with dual plane intake, small carburetor, and small cam to make the same hp. An effecient 540 will make 600-650hp (or more obviously)

Effecient (high volumetric effeciency) motor or innefecient (low volumetric effeciency) ? Which do you want.....

Based on what? This is a completely wrong statement. "Marine" engines don't need any more "air" than any other engine. Cross sectional area in a 305 is way more than enough for a medium rpm 540 (<6500rpm) and the as cast heads I did with a simple chamber blend flow 385 cfm @ .700". Your average 540 with a 230@ .05 cam will need less than 340 cfm @ 5500rpm. Those same 305's flow that at .500" lift with NO portwork. Bump the cam to 245@ .05 and the rpm to 6000 and you're still needing <350 cfm. 315's flow more air, but IMO aren't "better", just a lot more expensive.

HP will be about the same, (maybe less) but power under the curve will definitely suffer. VE will be way down with the bigger heads...cyl filling will suffer, and so will tq. as a result.

prove it,and on a real dyno.

Well I don't have to throw a rock in the lake to know it's going to sink. Some things are just obvious...at least to someone who knows what they're talking about (which I understand leaves you out).

talk talk talk,prove it.

Another head to consider for this build would be the CNC Brodix BB1. 305cc, fully cnc'd, flows 375 @ .700 with really good low and mid numbers.

Thats a wise plan.He's the real deal.

If you would like the correct info on which heads AFR says you should use on what engine size, go to their web site and read everything that they tell you about which heads to use on which engine size. Just as a little bit of advance info, they will tell you that 305's are to be used on 396-502 BB's. In fact they actually tell you that their 315's are for the same size (396-502). So either AFR is wrong, and some guy you never heard of is right, or AFR is right. As AFR has been doing heads since 1970 for people like Grumpy Jenkins and Junior Johnson, I'd stick with what they recommend.