I don't understand the thinking here. Seems like a lot of time and money to make a 454 out of a 425 Cad engine, when it would have been cheaper and easier to just buy a 500 Cad and drop it in.
I'd rather have a 500 Cadillac than a reworked 425 to make 454 c.i. And if weight is your main consideration, then I'd spend the money on a pair of aluminum heads to bolt on a Chevy 454 and use that to save weight. A 454 with aluminum heads will be lighter than the 425 Caddy.