[Steve Barcak]

What you wish to do can be done but...
I would suggest you using a stronger 389 or 400 block with 3" mains. There are inexpensive cast and forged cranks available for these 389 and 400 blocks in many strokes and you would end up with a stronger block, better oiling and a stronger crank. Piston and rod choice and cost would be the same as would other engine parts. You can build the 389-400 to the same size as the 455 too with the available stroker cranks. This is the way most people 'in the know' are building performance Pontiacs now by using 3" main blocks as a foundation for their performance engine now that reasonably priced and good quality cranks are available.
Your 455 has value and I would sell it as the very late blocks are not known for their strength. The 455 would make a great street 4bbl motor for someone else.
Even with a mild blown application, why not start with a better combo of parts? This would also allow for more HP if you decide you need more and give your more reliability as well for about the same money.