"yup it's basic math.. the smaller ports heads will make more power where he'll be use'n the engine..
your head choice will loose power from idle to 3000 rpm..
you know the rpm he'll be in 95% of the time.."
Considering that factory GM Oval port heads have runner volumes from 265cc-up, most are around 270cc-290cc I find your point invalid. Like I said before, it's not like I'm telling this guy to get a set of 325-365cc intake runner heads here. I'm suggesting that he look into a set of heads with runner volumes from 270-300cc. Which just so happens to be the exact same size range that you will find GM oval port heads. The big difference is the fact that the aftermarket heads have far flow characteristics, they create better velocity at all lift ranges and all RPM ranges.
putting a set of crappy flowing, small 265cc oval port heads on a 489-496 is about the same as putting a set of 434 non HO 305 heads on a 383. Sure will it run, yes, will it make tq, yes, would they be out performed by a pair of aftermarket 180-200cc intake runner heads at absolutely every RPM level, YES!!!
The set up that I have suggested here; Brodix 294's with a dual plane intake, moderate 750-850 vac sec carb, 220° cam, will run just fine with a factory stall, the power band will be about 1500-5000. I would estimate it's max tq would be made right at 3500rpm. I would hope that he is running atleast a 4.10 rear gear for a tow vehicle, with around 30" tires put him running 3000-3200rpm at highway speeds.
The GM casting heads with the cam someone suggested (213°) will make around 380hp/525tq MAX!, (that is likely generous) it will make its max tq around 3000rpm, so there for it will be making about 525ftlb of tq at 3000. Where as the set up I have given him would make around 485hp/625tq, as i already said it would make its max tq around 3500rpm so there for at 3500rpm it would be making 625tq, I would say that it will be safe to say that from 2000-3000rpm my set up will make more tq than the set up you are recomending. You know, the RPM he'll be in 95% of the time!
Please if you can't give good advice, dont give any advice
A cam similar to this would work well:
Howards Cams Retrofit Hydraulic Roller Camshafts 123515-10 - SummitRacing.com
You have to keep in mind that the manufactures rpm range estimation is made for a 427-454BBC, if you are going to stroke it to 489-496 that is a fair bit more cid, therefor you will need a bit more duration to achive the same rpm band.