You can still find 831's out there,NOS & used,but you have to look.
The #387 has a 3&5/8 outside diameter,shaft diameter 43/64.
The #831 has a 3&3/16 outside diameter,shaft diameter 11/16.
No,not all the repops are Gold cad.The current Delco Gold Cad plated repop is not a period correct shade for the late 60's-early 70's Vehicles on the assembly line.There are subtle design differences as well.
