A friend of mine has a formula 312 formula and is looking to upgrade the horsepower and is restricted by the factory swim platform, what has anyone done on a twin engine setup?

Yes done a 292, a 311 and a 312. The 312 is a bit easier. Just pull the box from under the platform and run whatever exhaust you choose. The tips are mounted in a std bravo location. The older sr1's are not and need custom tails or wedges etc.