Tim, Dave is right, you double the reading obtained on the V8 scale which is the 45 degree scale. But you probably already know all that. You count the lobes on the distributor shaft, which correspond to the number of cylinders of course, then divide that number into 360 and that'll tell what scale to use. Like a V8 has 8 lobes, divided into 360 is 45, so the 45 scale is the proper one. That's the reason doubling on the 45 or 8 cylinder scale works for 4 cylinders. If it reads 30 on that scale then the dwell is 60.
I've searched high and low through my factory manuals put out by Allis-Chalmers themselves and can not find a dwell reading for the WD-45. The old charts I have list several 4 cylinder motors but the range of dwell of course depends on the point opening, since that's what it is, how many degrees the distributor shaft turns with the points closed. So if the point gap is reduced the dwell will be higher. The four cylinder engines were listed as thus: 52-54, 28-35 and 50-57. So you can see there's quite a difference. A good way to get this for yourself for starters would be to carefully measure your point gap to the recommended gap of 0.020". Then start the engine and take your dwell reading. This would be a good base and point of reference for your future readings. Good luck and God Bless.