How to best determine if a bike will fit without riding it I would like to get a Surly Cross-Check but the local bike shop doesn't stock them. They have suggested a 56cm, but I am concerned about the top tube length (I am more legs than torso). Are there proven ways to figure out whether a bike fits other than riding it?
The best answer to your question is simply "no."  Unless you've ridden the exact geometry before, there's no great way to know if your body will enjoy the fit.  Sure, there are MANY adjustments you can do to any bike to get it close, but nothing replaces taking the bike out for 20 miles to find out how your body will respond.

Now, with that said, if you haven't been riding a bike on a regular basis and only plan on riding this a limited amount of time, a good fitter could make a reasonable judgment call without any serious problems occurring later.  The bike can be tuned to your needs, as long as the general size is correct.