The bottom bracket shell width is the standard 68mm, it's BB-6500 in there now. From the reading I did after this was posted, it looks to me as if the hollowtech II BB will fit in my frame just fine. I'm not 100% on this, because it's the first time I've dealt with bottom brackets, but the reading I was able to find looks like this won't be a problem.
So I went ahead and ordered this crankset. Thanks Elvo! Assuming this fits fine in my bike, with the new 12/27t cassette I'll have way, way better high-cadence climbing ability. Two weeks ago we did some 9% grades during parts of our ride, and with my 39t/25t ratio there were times my cadence dipped into the 30s, and I was mashing for all I was worth just to stay upright. The new 34t/27t ratio will make it far, far easier.
I'm especially interested in seeing how the bike feels with the 50t large ring up front instead of the 53. It'll compress the high end somewhat compared to what I'm used to, and that's exactly what I'm looking for. I'm still tossing around the idea of one of these days making a 13-26t or 13-25t cassette to compress it a little further.