News flash: Airflow Dynamics, aka, AFD, is just about to realease three new alloy heads for the Clevo.
Here's the AFD web site, although these new products are not up on the web site yet. Here's a post from last Thursday from AFD Dave himself to the Cleveland Forum:
The part about the price being competitive with Edelbrock: the Edelbrock Cleveland heads are about $1,980 a pair assembled, $1,400 bare, at Summit. BTW, most Cleveland guys say save your money rather than buy Edelbrocks. They flow about the same as a ported iron 2v head from 38 years ago, and not as well as ported 4v iron heads.
Regarding that 8000 rpm target, I don't think you'll make it with a 408. But if that's what you want and you also want it to hold up under road race (rather than drag strip) use, you should plan on starting with an aftermarket block. That means a Windsor block, from Dart or World Products. You can put Cleveland heads on a Windsor block without a lot of trouble, so that's not a problem. It is pricey, though, about $2000 for the bare casting. (There is also an aftermarket Cleveland block (9.2" deck height, dry intake) that's 6-12 months from production.)
You will then need a forged crank, preferably non-twist, or a billet crank, and the best H-beam rods you can find. You will also need a pretty wild cam, pretty much non-streetable.
And you will never get 650-700 all-motor hp at the wheels out of 408 ci. McKeown Motorsports Enterprises is offering a 427 ci Clevor with CHI heads that claims 650-675 streetable hp at the flywheel and costs about $12,000. But 650 hp at the wheels requires more than 800 hp at the flywheel. On the other hand, you can go to 454 ci with the Dart or World blocks. If you can get the same 1.5 hp/ci that MME gets with its crate Clevor, that would put you at 680-700 flywheel hp, which would be about 550 rwhp.
So go for the gold, that would be great! But there's a reason those Cup cars run as good as they do, actually two reasons. The first is money and the second is they're strictly race-only.