Bill. My casual following of 312 cranks on eBay indicates that a $300 'Buy-It-Now' price should provide a sale although you may have to list it more than once to reach a buyer.
IF you have not had the crank magnetically inspected, I would recommend having it done with a machine shop receipt to show for it. My recollection is that the cost on having the mag test is less than $50.
In working with the machine shop, I would steer them to pay particular attention to the crank snout connection at the first main bearing surface and the radius-es related to the first crank throw. Yes, the entire crank should be checked, but my understanding is that these particular area are more prone to problems . . .
Some may hesitate at the crank having been turned .030 under-size at both the mains and rod journals. Retaining the quality of the main bearing and rod journal radius-es is important for y-block crankshaft integrity.
Hope this helps!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York