I would really question 30hp from shorty headers without some solid dyno data on a like for like application. I suspect the head pipe shape has an influence too. The driver side one, due to clearance issues with ride height, steering and lining up to go past the m.c., is usually contorted in a way that's not the best for flow.

Those ram horns from Speedway look interesting, especially the way the outlet flange is "tucked in" for clearance. The overall design reminds me of the Y-block Ford truck manifolds from the '50's. With that high arch and the tuck in, routing the plug wires neatly might be an issue. The stock manifolds were pretty much a "straight" down shot, and the wires could be routed up from underneath. With that tuck in that may not be possible. And the high arch might eliminate most of the "ready made", over the top looms. It would be nice to talk to someone who's really used them for that point. BTW, Chevrolet is reproducing the rams horn manifolds in the 2" outlet configuration. If you shop around to some of the GM Performance dealers (Scoggins-Dicky, Sallee, etc) you can get them for something in the low $100 range each. They do have some extra lumps, and the generator bracket flanges on them, but some saw and gringer time can eliminate them. Originals are available at swap meets and on ebay, but the restoration guys bid them up pretty high. At three bills the Speedway ones are probably a comparable value considering they don't need the extra work.

If you go the tube header route beware of the cheapie ones available. Typically they skimp on the flange thickness, and are often built so poorly they leak from day one, or soon thereafter. I prefer a 3/8 thick flange plate, and milled welds at the tube ends. Costs more, but you're less likely to end up with that annoying tick-tick-tick leak sound. That is the nice thing about the cast iron ones. The flanges are less likely to warp, and the thicker material makes them quieter too.

As for hogging out the innards. You may already be aware of a slurry honing process wherein a clay like substance, loaded with abrasives, is forced through the casting to "hone" the inner surface. Here's a link to Extrude Hone for more info. http://www.extrudehone.com/