I authored a spreadsheet for calculating pincushion distortion, screen curvature, throw ratio and lots of other useful stuff based on screen height and throw distance only (that's actually all you need to know, plus an understanding of optics - which is my job).
If anyone wants to try it out, PM me. PLEASE INCLUDE YOUR EMAIL ADDRESS IN THE PM.
CAVX's broomstick is a good practical method, but the spreadsheet approach allows you to simulate your installation before deciding on a room size, projector model or where you're gonna buy the broomstick. Plug in your room ideas and play.