Looking at gravel racing what should I look for in fit compared to a normal road bike setup? I'm concerned about stack and reach angles of head tube and seat tube, bottom bracket drop, fork rake and such things.
"Road Bike" is a pretty broad term, but let's assume we're talking about a bike designed for long-distance road riding and not criterium or even road racing—a category used to be called "sport touring," but is now referred to as "endurance racing." Current examples include bikes like the Trek Domane, Giant Defy and Specialized Roubaix.
Also, it depends somewhat upon what you mean by "gravel racing." If you're referring to short events like Barry Roubaix that are at most a couple of hours, then a cyclocross bike would fit the bill as well as anything, especially if you already own one. The downside of using a cyclocross bike is that most are really designed for short, fast, off-road races and don't necessarily lend themselves well to all-day comfort or long, 40-mph descents.
There are a few cyclocross bikes that are designed to be less aggressive, and those are the ones that tend to turn up at gravel events. Current examples include the Trek Cronos and Boone, and the Surly Cross Check. The Niner RLT9 is marketed as a gravel bike but has a design that fits better into this category. My experience with this class of bike is that they require more effort to arrive at a good fit, and can feel more exciting than necessary on fast downhills.
"Gravel" bikes aren't all alike either, but the ones that are different than cyclocross bikes feature a longer head tube (for more upright riding position), lower bottom bracket, more fork offset and slacker angles. The best current example is the Raleigh Tamland, but the All-City Space Horse is pretty close too, despite not being marketed as a gravel bike.
To me, the best thing about "gravel" bikes coming into style is that they're actually good for a very wide variety of surfaces and emphasize comfort over raciness. Not limiting a ride to one specific type of road opens up a lot more riding opportunity.