Either choice would work well. I would personally go with the option of 3 8's. The reason is the 8's would have a much smaller mounting depth, and in an S-10 that might be an advantage when trying to design your box. Even in an extended cab, the big super woofers can be a pain to orient properly so that they don't have interference problems with the port, or something else in the vehicle.
The DD Toyota extended cab, with 4 DD 1508's (which is basically the same thing as the AQ SD2 8) and a DD Z1 is pretty awesome.
The only problem I see is that the amp would only being seing a 1.33 ohm load, and it's not going to produce quite as much power as it would with a single 10 and dual 2 coils, running the amp at 1 ohm. You should have enough more cone area with the 3 8's to make up the power difference, but you might consider saving a little more cash and picking up an AQ 2200.1 when it comes out, instead of buying the 1200. That would be a killer setup for that little truck.