I was just looking at a X-90, I don't think there is more room.
Looks like they made a one piece pan for the T51. Nice looking sump in the photo. For me the clearance was back drivers side cross member, and front right side on the diff. There is room to go outward on drivers side, except back corner. If you change shape of oil pans to provide needed clearance then you could have the room to drop the motor the inch that I need. (send me one.) Also you will need room to remove the oil filter.
As you have to build your own motor mounts, make up the diff mount at same time. Both me and Muskegtracker had tight clearance between the alternator and the right side frame diff mount.
Hood clearance issues were on the front intake cross tube. If you turn the manifold around and put smaller TBI's on the ends, are you then going to cap off the the original TBI spot, or run a smaller cross-tube?
My low end torque is great. Doesn't take a lot of throttle to break my tires loose, and 100 has lots of throttle left.
I used 2003 precats & exhaust headers, as they were smaller than the 2005 ones. As you were planning on a stand alone computer system, you could put the cat under the car, if you install one.
I put a 4 link in the rear end, and it does improve the handling. Still with the power I have it likes to jump right out there. If yours spools up fast, it could get away easily.