Their rear ends are probably setup to be used with their mounts. Which does you no good since you're a nonconformist.
Used to run into this a lot with lifted 4WD trucks when the u-joint angles got too severe the engine/trans mounts and pinion angles had to be changed. Your u-joint angles can't possibly fall into this category though.
The centerline from the eshaft to the back of the transmission output shaft has to be in the same plane as the pinion shaft. Is moving the front of the engine up or the back of the transmission down at all feasible?
A good guideline
http://www.iedls.com/asp/admin/getFi...&TID=28&FN=PDF
Hope this helps, I really need to see this at Deals Gap.