Hi All
As stated above i have tried to do this mod on my car,
Reasons why - 20v branch have great design and proven to work well, also keeping to the 4-2-1 system was a great gain due to over price 4-1 branch and a custom made branch with unknown areas of gain.
20v branch bigger on the ID of the piping even the down pipe section is bigger then a 16v stock system

Any way problems i came across and solutions -
1. The outer mounting holes of the branch does not line up to the 16v -
MOD - drill outer holes and it will work
2. After doing step1 we now found that the flange is touching the dizzy heat shield and the mounting holes for the heat shield of the branch is also touching the dizzy-
MOD we had to cut of the branch heat shield mounting and trim the flange
3. The last problem stopped us, it was the starter that was in front, one of the piping had been full on it and this didn't allow us to even get the flange to the head -
MOD get a 20v starter and relocate it to the back.

All in all the branch does fit, but due to lots of mods but still think it will be less then buying a new branch