That's an admirable trait, but the problem is, you have chosen one of the worst possible engines to try to do that with. The narrow (small) bore center spacing of a /6 hamstrings all efforts to try to put decent size valves in the motor, and the fact that the ports were designed for a 170 (and, they were) doesn't help any. The only engine I can think of that is a poorer choice for trying to go fast, normally aspirated, is a 144/170/200/250 Ford 6, with the integrally-cast, intake manifold.
By whose calculations? I'd like to see documentation to back that up. I don't doubt the slant head needs help, but with the right person behind a grinder and on the flow bench.......again, I'd like to see the data. I know someone who is approaching 200 CFM now at around .500 lift with a slant head with just conventional porting. That's flowin for a slant.
The "big" Ford 6 (240/300) has much larger valves, and can be fitted with Cleveland, welded-up, V8 cylinder heads (which have humongous valves,) if you don't like the stock head, and the 250/292 Chevy 6 is also another engine (which also has a 4" bore) and can accept large valves. It also can be fitted with the V8 cylinder heads, if you don't like the 6 head.
The phord valves can be fitted to the slant too.....but IMO they aren't needed. I think they are too much. Those 1.70/1.44 or the stock 318 valves are probably good for most anything. Remember the bore size here. It ain't real big.
The /6 can, with forced induction, run toe-to-toe, with either of these brand X engines, because of it's unusually strong infrastructure which allows LARGE amounts of boost to be used without damage to the reciprocating assembly, with 500+ HP fairly easily attainable, as evidenced by Ryan's and Tom Wolfe's cars on FABO.
Ed's not buildin a forced induction engine. So the point is kinda moot what a forced induction engine will do. That's comparin apples and oranges.
But, because of the lack of a really good breathing head (and, I'm not sure that's ever going to be possible, due to the close bore center spacing of the /6 block,) trying to build a normally aspirated /6 that has specific output numbers approaching 2 HP per cubic inch, or even 1.5, is like trying to run a marathon with your mouth sealed with a piece of duct tape.
Mark's car still amazes me... It's a rocket, for what it is!!! Love to watch it run...
