It sounds like you have a good plan and done the right steps. An oil change would be good. Use a high zinc oil since you don't know how much time is on the rebuilt engine. Valvoline VR1 is what I use. You should notice a load on your drill motor when pressure starts to build in the pump. If...
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I mostly use full-strength Simple Green and a variety of nylon, brass, and steel wire brushes. Pressure washing, if you have access to one, is great for getting through the heavy stuff.
If you haven't already, get yourself a copy (digital or paper) of the 1972 Ford Shop Manual set. It provides illustrations and has the procedures you'll need in easy-to-understand language.