1. Don't cut the surrounding plate. The rod that goes from the shifter pivot point to the tranny shift shaft shold be bent somewhat to allow clearence. If not, you can remove the rod and bend it a little more. That way you can fix the problem without cutting anything.
2. When you really want to fix the problem switch to a good synthetic ATF. The engineers at Mobil recommended Mobil-1 synthetic ATF and I did so - the first gear grinding is significantly reduced. In fact, I have not experienced it since doing the switch. I would advise you to go buy some Mobil-1 synthetic ATF and try it. There have been so many threads on this it brings me to the brink of madness to even think about it, but you might want to do a search.