You would also do well to take a "large pin" lower ball joint with you - besides the sample older spindle. The taper on the ball joint pin needs to be fully seated in the upright - and have its threads exposed the same amount. Depending on how far into the boss you enlarge the taper - there may (or may not) be a need to put a ground flat washer under the slotted nut. The taper on the Ford pins is a 1.50:12, which is referred to as 7° - but its a little bigger (7.153°).