Short Answer:
ProSD, yes and yes.
Long Answer:
The *big* diference between the ProS and ProSD is that the lens mount has changed (and is reflected in the KL line of lenses.) This allows for the 500mm and 75mm PC lens. *IF* you plan on using these lenes or the price diference is negligable, ger the SD. If not, go for the ProS (though it is an older model, produced from 1974 to 1990 when the SD came out.) All RB back can be used with the Pro(S) back can be used on the SD. I prefer at least a ProS back because of the interlocks and double exposure switch.
Either way, you are about to buy a great camera.