getting a wrist rest the right height for the classic, especially if you intend to tent it, is almost impossible in aftermarket sources without alot of modding. 'bolting' a rest on sounds easy only if you plan to use the ergodox flat, but otherwise, prepare for a lot of work. It is probably easier to just get some thick leather pads and wrap it around the fullhand rests for some extra height if needed.
I bought both the fullhand and a classic (the classic is yet to be assembled), and I can say the fullhand will be better in terms of wrist support. The only reason to get the classic is due to the small size - makes for easy transportation.
@mashby, like glod and sordna said, you can get both by doing 2 transactions, or just talk to the massdrop guys. They'd be able to help you with that if you have any problems.
anyone interested in the ergodox should probably jump in at this second round - while the keyboard is great to use, I just don't see a lot demand for this to get a third round in the very near future.