I did it in an early b. So I had to use the universal kit. Plus I made it harder and had a poly 318.

It took 2 weekends to do it.
Got everything mocked up in the engine compartment, and took it to a local shop to cut and crimp the lines.
Then had a plate welded to bolt the new box to, with studs that bolted where the orignal heater box bolted to.

I did not use the stock controls. I removed them and put in the electric controls, so I don't know how hard it is to get the stock heater controls working. I do know that it is backwards. Heat on the slider is for cold and cold is for heat, so I opted for the electric controls.

The hardest part for me was getting the compressor lined up, but for an engine they make the kit for, it should be a bolt in.
They supply a pulley that bolts infront of the crank pulley, and everything runs belts to that.

It would be nicer if you could find an a/c donor motor for all the brackets and pulleys so you don't have to use much of their motor mounting stuff and make it cleaner looking, but you do need their plate(at least sb wise) for it to bolt to.

Inside I image the a/c box is the same, just mounting hardware is different.
It is a lot smaller than the 66 and up a/c boxes. It was smaller than the 65 heater only box, and that is about half the size of the 66 and up a/c box.

There are several people that found a/c dashes and mounted stuff to it. I chose just to hang the vents under the dash.