Me personally would be more concerened with compression ratio vs fuel octane. Cast cranks have been used for years and if you were running compression ratios in a range to run pump gas I sont think you would have problems with a cast crank. The engine you have listed only has 8.0:1 listed. not much. Bump that up a little and you could add some nice grunt to your engine. Listed at the bottom of the spec sheet on that 454 is says for X dollars you can bump it up to 9.0:1 and add 30 HP. That sounds like a good deal to me.
As far as the prop goes, I am no prop expert but I dont know about a 2 blade for that application. You didnt say what size blades you are looking at. I just put on a 78"-3 blade whirlwind. I have a zz3 small block that is stock for now and with it's 345 HP. it turns the 3 blade fine. It is set at a low pitch but I would be afraid that with a torque monster like a worked over big block you would not be able to get enough pitch in the 2 blade BUT I would call the manufacturer, they could tell you.
Tim
PS: I am running a 2:1 belt drive on my boat.