That pulley is salvageable by a very good welder who is familiar with repairing cast iron. Don't discard it. It can be patched and machined back to its original shape. The GMC crankshaft has the same diameter snout as Chevy engines- - - - -1 1/4" diameter, so you will have a pretty good selection of possible replacements. I have a 228 engine stashed away in my storage area, but I'm pretty sure it has a completely different front balancer/pulley arrangement. Unless you're planning on pumping a lot of water at full throttle, I doubt if there's much danger of crankshaft damage in a restored vehicle.
A lot of the older fire apparatus trucks were called "bumper pumpers"- - - -with the fire pump driven off the front of the crankshaft, so unless something else went wrong, I doubt that moderate loads applied to the crankshaft snout would do any serious damage. I've also seen inboard engine boats with V-drive units that use the crankshaft snout to power the propeller.
Jerry
