I always advise the first two things that need to be determined are 1) A performance/HP goal, and 2) a budget.
Since you already have a pretty nice stash of parts to work with, I'd lean towards a 454 build, or even better as Al suggested above, possibly a 489/496 stroker build. I did exactly that with the engine in my Chevelle--rectangle port closed chamber heads, solid lifter cam and a 163 intake--and it easily surpassed my expectations with plenty more left in reserve (and I'm not done with it yet either! [img]<<GRAEMLIN_URL>>/wink.gif[/img] ) .
You can read about it
here if you'd like.