looking for new exhaust system.
there are some companies offering aluminum merc-style exhaust manifolds and there are headers style stuff.
aluminums are 1/3 price of the headers stuff

which one would you use?
bb-520 cu-blown

ttt

For that much HP, you'll need headers. I'd call CMI and see what they recommend.

I have some like new Eickerts only 4 hours fresh water lake use!!!

With a blown application exhaust in not as critical as a naturally aspirated engine. I have seen people run gil offshore or Stainless Marine. The aluminum aftermarket systems tend to hold up better and absorb vibration better. I would ask around some more before you go and spend so much money on headders.

I wonder if some others have seen this as well?