Could I just put 1 cutout in my 3 inch downpipe?
Yes, you can. This is my setup...

i know this is a mustang forum but on my turbo sentra i used a boost activated cut out and it worked great. no need to worry about the engine failing or having to open it up. it uses a waste gate bracket setup. the thing opened at about 10 psi of boost and worked great. it was made by ATP 3" in and out.
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