As for your trans swap. I's shake loos the bucks for a Lakewood bell that has the T-5 pattern so you can retain all your original clutch linkage setup to ease the intall. The T-5 uses the same # of input shaft splines as all the other Ford trannies, 10 i believe. The only things you'd have to worry about would be the length of the input shaft into the pilot bushing. Not really a big deal as you can custom make bushings and even "extend" a bushing if the input is too short. If it is short, then the '94-'95 input shaft swapped into your T-5 would help remedy that because it's a tad longer.
I haven't done this or really looked into it, but you might be able to have the current bellhousing drilled and tapped for the T-5's pattern aswell.
Keep in mind that the shifter is non-adjustable and can sometimes be a problem.

For fuel delivery you'll need to have your gas tank modified to accept a high pressure in-tank pump to fuel the FI. Wiring up the computer is not a real big deal. There's plenty of Mustang sites that have this info redily available.

I'll have to agree with screemer though... those big Galaxies were ment to be FE powered.