How did the crank break?

hmm, internally they are VERY VERY similar. The cylinder head ports are also VERY similar. I would suggest pulling the vortec block and checking for any damage. The intake, blocks, and heads are NOT interchangeable. Almost everything else is. If the block isn't damaged, then consider simply swapping the crank, rods, pistons, from the LT1 to the vortec.

The iron head LT1 was rated at 260hp and 330tq. The vortec 350 was rated at 255hp and 335tq. The differences were in the cam and intake manifold.