360 magnum

I picked up the 360 magnum on saturday. A real clean motor with 81000 miles. When he pulled it for me he didn't cut any wires, unplugged them all.
I have the computer, all the wiring from the engine compartment and the gauges and all the wires from the dash. I would like to keep the fe when i put it in my 67 fastback but it doesn't look easy. I biggest consern is gas mileage as i plan to drive it as much as i can. Will the fe improve the mileage a lot over a600 carb?
I also got a 8 3/4 posi 489 case with 294 gears for $250. I think that the
stock magnum will have enough low end power to handel the 294 gears.