There are big advantages of going to a 5.9 magnum. I posted above about my 408 but would change a few things. The 5.9 base with roller cam and stock rockers were used in the 380 hp crate 360. A 408 version with a cam similar could use stock rockers and lifters if there are new stock replacement head castings are available. Some minor bowl work in the ports, topped off by a fuel injection system would be my choice now. Should still make 450 hp or more and be a lot more budget friendly.