Again, an old thread, but info is always good to make public. So, I measured a Boxster engine (which has the same footprint as a 996 engine, but has a shorter intake system) and it is only 20 inches from teh bellhousing mating surface to the front edge of the pulley. The Boxster front engine mount comes a few inches further forward than that. Also, I measured the width of the engine across the widest part to be 35 inches. I would have measured the hight of the engine too, but the intake system wasn't in place and the measurement would have been of limited usefulness.

I still have access to the engine for a few more days if anyone wants any specific measurements.