So I should have about an inch of pincushion on the edges of the screen that I need to overscan?
You should also add in some extra overscan for 2.40:1 movies.
2.40:1 movies occupy 800 pixels out of 1080 pixels of image height. When the image is vertically stretched, however, the middle 810 pixels will be stretched to fill the height of the image (810*4/3=1080). So between the 800 pixels of a 2.40:1 movie and the top (and bottom) edges of the image there will be a 10 pixel black band.
To get rid of this thin black band you need to optically zoom the height of the image a little more than you might have thought at first. The ratio is 810/800 = 1.0125, one and a quarter per cent.
So, to fill your 60" high screen height you need to zoom it so that the 16:9 grid pattern (or whatever test pattern you are using) enlarges to 60*1.0125 = 60.75" high, an overlap (dividing the extra 3/4" equally between top and bottom), around 3/8ths of an inch top and bottom, say 1/2 an inch to make sure.
To prove it:
800 pixels represents 800/1080 = 0.740740741 of screen height.
Now multiply 60" by that number and you get 60*0.740740741 = 44.4444" BEFORE
vertical stretch of 4/3 times.
Putting it all together 44.4444*1.0125*4/3 = 60". Your 2.40:1 movie now matches your exact screen height. 16:9 material will overshoot by a little.
I always recommend adding a little to this to make sure. Adding some extra also accounts for 1.85:1 Academy Aperture films, which are slightly shorter (at 1040 pixels high) than 2.40:1 scope presentations are after vertical stretch.
I know it sounds complicated, but I've seen some unfortunate installations where everything is bolted into place, only to find that the image doesn't quite fit the screen and, because everything else is maxed out, can never
fit the screen. You need to be aware of the issues.
A1920 x 1080 test pattern showing all the common movie apertures is at my web site: http://www.xeitopticscom/test-patterns/