When you are out cruising, who would know it's a 6 ?.
Most people think all Mustangs are V8's, but you'll be laughing with the fuel savings.
Engine and suspension parts are pretty much Falcon and readily available. Generator will be OK providing you don't do all short trips, but a Falcon 6 alternator can be fitted for more charging amps.
Take the car for a good drive before committing so you know you will be comfortable with it.
If later swapping in a V8, you will need to change the wheels, front axles, diff etc from 4 stud light duty to V8 5 stud running gear, to be legal for rego and insurance.