340/727 and 440/727 can you use the same driveshaft-changing a 71 Road Runner that had a 340/727 combo to a 440/727 combo-will the driveshaft interchange-the car has an 8 3/4 rear end thanks Daren

yes as long as both 727 have the same length tail shaft housing

meausre from mount to end of housing

should bolt right in same yoke and length

Will fit.I have done the same thing on the same kind of car.

It will fit but if the car has the small yoke u joints in it I would think hard about upgrading to the larger ones. I had a 69 B body converted from small block to big block and the diveshaft lost a front ujoint at 70mph with 4:10 gears and it was not pretty. New driveshaft,trans,radiator,and the stock 10" drum brakes were scary as this pos was breaking up under me.
Lots of changes and upgrades since and the stock driveshaft was rebuilt with new u joints not too long prior just wasn't enough this time. You can do it but if you plan ahead and upgrade the car before you break stuff it is easier and cheaper