Actually, the crank CAN be reused. But it has to be welded and turned. And then I would suggest having it nitrided again to harden the surface that has just been reworked. But it really depends on the depth of the scoring.

If it is 0.030" or less in depth, the machinist can turn the crank down to that level, and then thicker bearings are used.

My suggestion is to take the crank to a good machinist and see what he thinks. If it can't be saved, then yes, you can find a new crank for a few hundred bucks.

Expect to have the new rotating assembly rebalanced. Especially if you're replacing the connecting rods because one broke.

Another note on the bore...the 327 also used a 4" bore, but unless the engine was changed to a 327, they were not installing 327's anymore in 1979, so you probably do have a 350.
And if you rebuild the 350 0.030" overbored, you will have a 355.

52 GMC 3/4 ton pickup
68 Big Block Vette
68 455 Firebird