... This may explain why the outlet hose is dangerously close to the sub-frame and night wear over time.
The rigid elbow for the return hose should not be pointing up. It should be loosened and then pointed to the side (left side, toward the wheel). This should give you more clearance.
1. Is the old long mount retained?
Yes. The goal is to make sure the gravity-fed nature of the setup is maintained. The feed line of the pump should be at or slightly below the bottom of the fuel tank.
2. Does the 3 finger circular mount plate bolt directly to the subframe or is there another plate I need to get?
I've seen both kinds of setups. However, I do believe that the correct setup ought to be to connect the new plate directly to the old mount plate, followed by the rubber mountings, and then the pump. The new plate has several choices of holes to use for mounting (this will be clear once you've removed the plate).
3. Pictures would be a real help!
The following image is taken from our Technical Manual (page:
http://www.sl113.org/wiki/Fuel/FuelPumpRebuildLater). Note that the perspective from which the photo has been taken is different from yours.