I lay the colums in floor on 124 cars and pull the wheels on 140's. The entire dash pads has to come out, along with the other stuff mentioned further up. Go ahead and replce the foam looking evap drains while your looking at 'em. (had 2 140's, 3 126's and a couple 124's with weird electrical gremlins from wet floors due to bad drains)
I'd do all the elements.
ACM makes the best fitting core I've seen and most have a expansion valve already attached. Just dont do what I did one day and decide the lines at the valve dont need tightening.