new build
I would also suggest seeking something other than the 847 (What brought you to that conclusion? Hopefully not the sound...). Go with a custom grind from whatever cylinder head company you go with as they will know best, not the old-school GM grind from yesteryear.
As far as the bottom end is concerned, I would suggest doing a search and talk with a few local engine builders too. You will find immense amounts of info, but you are on the right track with seeking a forged bottom end with the nitrous you'll be pushing through it.
Good luck.
If you pick the cam, one guy ports the heads, another guy specs the valvetrain, another guy tells you what compression to run, another guy tells you what parts to put in the bottom end, another guy or you does all the work...
See where that's going and how easily it can turn into a disaster?
I'll say it again like I and so many others have said before. A well-performing combo is parts that are designed to work together. Not a hodge podge of go fast stuff.

