well.... this forum is geared more toward W body style Grand Prixs.
Why not rebuild the 428? Or find a Pontiac 400 to shove in there?
I can't say if the Olds block will mount in the stock Pontiac locations. I'm guessing you;ll have to do some work.
And if you have to go the trouble to fab up mounts why not find a nice LS small block?