not sure what size exit your s475 has, but my old and new Garrett both had 5" hot sides. That 5" pipe reduces to two 3.5" pipes and then quickly two 3" all the way to the rear. On the cold side its 3.5" thats reduced to 3" immediately. While you might be able to go smaller on either....I wouldnt go too much smaller.
As for a fuel pump, I run the aeromotive A1000 which has been fine for carbureted use. I'm going to have to upgrade to go fuel injected, which is what I want to do eventually. A good used A1000 can be had for $250.
My intercooler has 3" in and out. I'm not really sure what it was rated at since I bought it with the car. When I put it all back together I'm hoping to put pressure gauges before and after to measure restriction. The intercooler makers seem to list their products by the HP it supposedly will flow up to. Not sure how accurate that is....guess it depends on the company.
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