Simplex rims are bicycle rims, not motorcycle rims. A servi-cycle rim is 22 1/2" OD. The bead seating surface is about 21 1/2". A motorcycle tire has a much thicker bead. That said, I don't think it will fit.
I have fit a 2.75 X 21 motorcycle tire onto a SPORTSMAN rim, but those rims are 21 3/4" OD. The tire does not fit well, too loose. But, and this is big, there are NO Tires made to fit the Sportsman rim.
If your looking to save money over buying the Simplex reproduction tires, just buy a bicycle tire and ride accordingly.