You have a couple issues to deal with doing a 440 RB big block in an A-body Cuda (1964-1969).

With the exception of the damn near hand built superstock Hemi Cuda's the largest engine from the factory in an A body Cuda was a 383 B big block. Even then, the 383 Cuda's required special mounts, single application exhaust manifolds, and an offset master cylinder mounting plate (brain is fuzzy on that last one).

The 440 is a tall deck block so you will be losing even more space between the shock towers and will most likely have to do some serious sledgehammer massaging to get it to fit.

About the only choice you have for exhaust will be fenderwell headers which will put you into needing to run skinny (like Moroso frontrunners) front tires. I have seen people do some nasty bandaid exhaust on A body big blocks by putting the skinny flat log exhaust manifolds on and using two right side manifolds. The driver side manifold gets put on backwards and the pipe comes down in front of the K member.

For your 8 3/4" rear end, go find a V-8 Dart/Duster in the junkyard for the housing. I think if you go with a 1972 or later rear end, this will also give you axles that are the 5 on 4.5" bolt circle to replace the 5 on 4" hubs you have now. It probably wouldn't hurt to grab the spindles and suspension parts also so you can put disc brakes on the front.

There is a manual disc master cylinder that is a standard application for the 70's A bodies that will give you a little more room without the power vaccuum booster.

You will be swapping the K frame for any V-8 replacement engine, or you can use the engine swap mounts with the 6 cylinder K frame, although I have never used the swap mounts so I have no idea how well they will fit.

You will probably have an easier time finding a 400 (that can be stroked into a 447) and it will be an easier swap than the 440 into an A body.