The head design actually really isn't good anywhere. My only guess is that it was cheaper than the 12 port design and they had already been doing it like that forever. For low-end power (and economy, for that matter) you'd like to have long runners of a relatively small diameter...the siamesed design essentially has no runner. The shape of the ports themselves is also pretty WTF...thus the bolt-in lumps to help that.
Another thing to keep in consideration is that even the 292 is a fairly small engine; the fact that it made all its power at a relatively low speed is kind of the reason it works as well as it does.
Maybe it's just me, but I don't really see going for N/A HP to be that productive with a 292 (or 250, etc.). The head/intake design is poor and it's just very slightly larger than a 283 is. I know the port lumps are supposed to help some, but it's still really pushing rope up a hill (IMO).
If I wanted to try to make any power with one I'd stick a junkyard turbo setup on it (I actually plan to at some point...should be fun).
I like them, but not really as a N/A hot rod engine (or for heavy towing and stuff like that). The small displacement and poor breathing kind of kill it for me.
http://www.hotrod.com/cars/project-v...ckage-install/
That first dyno run is pretty much the engine I'm putting together for my '68 Impala. Just a 350 with Vortec heads and a mild $100 flat-tappet cam...apparently you get 371HP and 409FTLBS through mufflers from that combo.
http://www.hotrod.com/how-to/engine/...-collar-build/
And there's pretty much the 454 that's going into the truck. Just a turd-o-matic oval port 454 with another $100 cam...408HP and 511FTLBS (I may use the existing peanut port heads on mine if the oval port heads I have need work).
As far as fuel economy goes, the much better head and intake design gives the bent engines a pretty big advantage there IMO. Not that I think that a 292 will burn twice the fuel of a 283 or anything, but the SBC has the edge there. I'd also have to imagine that when you start camming them up this will probably become more of a factor.