Yes, all Pontiac engines from '55-'58 came with forged cranks. I've heard of a few cases that were cast but, of the dozens I've seen they are all forged. It is easy to confirm, just look for the wide parting line and absence of sharp edges as in regular Pontiac castings. Even 389 forged can be found with some effort.
Tom S- Was it you that mentioned that you saw a 347 cast crank?
Steve
www.pontiacheaven.org