Another easy way to tell if it's a forged crank or not is to hit the counter weight lightly with a hammer. If it sings like a chime it's forged, if it makes a "thud" sound it's cast.

I'm currently building a 396 350HP for my '69 El Camino. Block and heads are from '67, heads are closed chamber oval port, pistons are a 19cc dome, solid cam with 240@.050, 10-1 compression, ported heads flowed 270cfm @.550 lift, has the forged 366 truck crank(rebalanced), 750 holley, Air Gap RPM intake, desktop dyno said 480HP-490Torque not accomadating the port work. The heads also have the chambers polished so I'm hoping to run on 91 pump gas. Just can't wait to drop it in. Hope this info helps on your build.