Well the carb swap would be the easiest but the fuel injected one isn't that hard, just swap the ECM and wiring harness, and a few small re-wiring issues. The AOD and M5R2 bolt right up to the 302 and you can even use the tbird LX motor mounts for the 5.0L and it will fit right in. You should also use the tbird accessory brackets and tbird oil pan. Best bet is to get a V8 from 91-93 LX 5.0L TBird and then rebuild it with better heads, better cam, forged bottom end and higher compression, and then spray a 200 shot at it. With the right cam, gears, convertor, and tires you could have an easy 11 second car. If you built a 450 hp 347 stroker and supercharged it, sprayed it, or turbo'd it, you could do mid-low 11's very easily. 10's would be do able but it would take some weight reduction, and some driving practice. It's possible. Dave N. is VERY close to running 10's with his 93 SC w/ a 347 turbo motor. I believe his is pretty much full weight too. Even has working a/c if I recall.
It might be easier to buy a V8 LX and put the SC gfx and bumpers on it, and then build the motor if you don't feel like messing with the wiring. I'm lazy and hate wiring. I'm swapping a 460 big block in my car and it will be carbureted. I was considering using a truck intake, ecm, wiring harness, and then putting in bigger injectors and maf, but i'm not sure if the truck computers can be tuned or not. Still it'd be easier to put a fuel cell in the trunk, run some lines, to an old school fuel pump, and then up to a carb. Can tune fuel flow, and idle easily. No need for idle sensors, mass air flow sensors, cam and crank sensors, throttle position sensor. Need more fuel, turn the screw or rejet the carb. Idles too high? turn back the idle screw.