Building a 598 NA motor it is going to be 850 HP or so what size headers should I use will 1 7/8 work

I think 1 7/8 will "work", but, I think 2'' or 2 1/8'' would be better.

My exhaust program is at work.

For now, without that and without any more engine info, i'm gonna' guess minimum 2 1/8", more ideal of 2.25"

1 3/4" is for mild 454's and smaller.

Stainless marine 5 inch

He's asking about primary tube's....although he didn't directly state that.

I would say 2" would be min, 2 1/8 would be best

What's the details on the build?