Two thumbs up on this build Atvguy!!! You have all the top parts kicking over there! My build has been a long time coming, not that long but it's been some time that's for sure!!
I can give ya zero input on exhaust.
As far as radiators go.... can't help ya there too much either(LOL). But what I can tell ya is I have read plenty on this site about radiators & everyone has positive to say about both. Some use the "cheaper" Chinese rads online & swear by them, saying they run them on the big bore motors with no issues. Others swear by the AFTCO & PWR rads, those are expensive. I have no idea on NACS rad. I think it's all up to you bro, me personally I've made up my mind & am going to buy an expensive one.(I was debating contacting you on that PWR...hahaha) Keeping your engine cool is an important part of keeping a proper running engine! Do you have a temp gauge you can run?(I don't know why I even asked... you prob have 5 on the shelf!). More air/coolant.... that's what I'm shooting for. But like i said.... people swear by the Chinese ones!
I hope all the information I DONT KNOW helps ya out somehow!