I saw this on an old youtube video today. The guy used the crankshaft of his engine to align the parts of the pulley. I wouldn’t use a good engine, but I do have a blown Kohler that has a 1” crankshaft. I’ve been wanting to see what is inside that engine anyway, so I may tear it down. At least I’ll have a pulley building jig (the crankshaft) when I finish.
Anyway, what he did was cut the parts of the stock double pulley to get the part with the key and used the crankshaft as a jig to align the pieces for welding.