sbc buildup

[kilrcam]

Ok guys i need some help here. I have a 400 sbc in my chevelle it's putting out around 550 hp. But in the past few weeks it has developed a knock. I have checked everything out and it seems to be coming from the bottom end. So i guess it's time for a rebuild, so here is my question. Should i build a 400 or should i go 383? My 400 is a 2 bolt block. I just bought a set of 200 etec heads and have had them on there for only about 3 months so i will be reusing these. My plans are an engine with about the same hp as what i have now N/A, and then adding a power adder of some sort. What do you guys think and why? Thanks for your help.

Brad