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.
An approach that can give you some confidence is to measure your existing bike(s) along the critical dimensions to see how they compare.
To my mind (and apparently also to the mind of the late, great Sheldon Brown) the most important dimension to consider is the top tube length. Basically, you can get a certain amount of adjustment in "reach", the distance between your saddle and the handlebars by adjusting the saddle on the rails, and the stem you've got, but the range of variability is quite small. Seat posts can be extended through quite a significant range, and you can generally play around with the rise on the stem, as well as the spacers on the steerer to get a lot of vertical adjustment.
So, download your specifications for the cross-check and we find that the top tube has an effective length of 570mm. Go out and measure the top tube of your current bike (or a bike you are comfortable riding) and if it is close to this, then you are good to go.
Many bike shops do a 'fit' session. Maybe more common for roadies but still useful for any rider. They'll measure you, watch you ride (video probably) and then come up with measurements that you'll be most comfortable on. Those measurements can be matched up against the bike.
My LBS charges $75 but I've seen places charge up to $300.