LAST UPDATE AND EPILOGUE:
SUCCESS!!
I was finally able to locate and purchase a used crank (Briggs # 493633) in very good condition that will work in our engine. I felt fortunate to have a seller that provided very specific measurements and good photos. At $ 32.00 shipped I felt I did pretty good. I have already test fit the crank and it is fine EXCEPT...
..this crank was out of a 1991 Briggs 3 HP with electronic ignition ("Magnetron") so it does not have the ground/machined detent into the crankshaft for the points plunger to ride in like on this 1973 Briggs 3 Hp with points and ignition. So..... back to Ebay and I purchased a Briggs NOS OEM 3 HP Magnetron coil for $ 30.00 shipped which seems like a very good price.
Michael