Troy,
I've been very far down this path before, with a SBF rather than a Chebby, but I can share a few experiences/observations.
1. The shorter the stroke, the higher she can rev. There's two reasons why a ferrari V8 can rev: a) short stroke, b) overhead cams and good valve gear. You won't get a chevy engine to rev like a ferrari w/o building it significantly oversquare, and using overhead cams. Without those two design elements you're going to be limited to something like 7K, maybe 7,500 with really strong valve springs.
2. The toughest part of the project is not the research, it's the getting-it-built. It's easy to armchair build a flat crank V8 based upon an American V8. What's tough is finding a capable and competent shop to build it, and then actually building it. Call around....you'll find that nobody really wants to take that on. Why? Well, no Ford or chevy build shop has any experience with that.
3. Be prepared to spend a LOT of money on the transition from theoretical design to actual build. Build shops don't work for free and there's a million issues that come up in the actual build. You'll find that just giving them specs is only the tip of the iceberg as far as what they need to know to actually build a crank and cam and rods/pistons. When I say "build" I don't meaning building the whole engine, I'm just talking about producing a crank and a cam.
4. People will tell you that it will shake your teeth out. That's just not right - ferrari V8s, for example, run quite smoothly with no need for balance shafts or any other other compensating device. If it does vibrate like crazy when running then that's a design flaw, not necessarily a problem with a flat crank V8.
5. Take a look at the new Ruf V8 for porsche - it's flat crank and very smooth running and has some interesting design features you may want to incorporate.
6. Be prepared for a lot of set backs and extra costs and push back from builders. Builders make money from cranking out a good volume of their standard builds. They hesitate to take on really unique projects like this because there's a worry there will be a lot of (uncompensated) time consumed in add'l design work, and re-work/returns.
I spent over $15,000 trying to get crank and cams built for a flat crank SBF, and had little to show for it in the end. The idea was to get a crank built suitable for a SBF, and two different cams so I could experiment a bit with cam profiles on the road.
I definitely see the value/intrigue in a flat crank V8 based upon an American V8, the main appeal (to me at least) being: simplicity and cost. Sure, you could put a F430 engine in your SLC but then you're stuck with buying $1,000 distributor caps, $1,500 water pumps, $12,000 valve jobs, $1,500 alternators, etc. That all just sucks.
Good luck with the project!