I am upgraging the exhaust on my 454 mag to a set of gil headers and am running into a space issue. I can only trim an inch or so off my silent choice and need another inch. Can I carefully trim an inch or so off the riser without screwing it up or affecting the performance? Thanks for you input.

I would not,Ran into the same issue with my Formula it had Corsa non-switchable.I just plugged the prop exhaust (CP Performance makes nice plugs).And ran strait 4'' exhaust hose.