[SFfiredog]

I have built some Boss 429 stroker motors, mostly for boats. Boss 429 blocks are usually thick enough in the bore to go to 4.5" I did have one "T" motor that would only go 4.44" safely though.
If you have the block sonic checked and it checks good with at least .150" to .200" cylinder wall thickness at 4.5" you could go 4.5 bore and 4.5 stroke and get 572 ci. At 4.44 bore with a 4.5" stroke you would get 557 ci. Cast steel crankshafts are readily available or if you have the money you can go with a custom forging or billet ($$$$$$$!). There are many variables and unique procedures that need to be followed when building a Boss.
Fell free to e-mail me privatley and I can help you with your combo. The weber manifold is way cool but the 48 IDA carbs that are available (no more 58mm) have no chance of feeding enough fuel for this motor.
I would get the manifold and convert it to 8 stack electronic fuel injection.
Good luck with your project.
Mike Braun