NEVER use a grinder or a angle grinder to take off the guides because the damage you make is high and it can even weaken the frame.
Most of the guides and braze-ons are put on with a blowtorch and copper or silver.
The same burner is hard to find and expensive on gas, also the change to burn a hole is very likely.
The best is to use a low temperature burner often used for copper plumbing and take the time to heat the part you want to take off dark red.
When it is possible put the frame in a vice the hold firm.
Take the time to heathen it up slowly and wait until it is really red.
Then get a pair of pliers and get a good grip on the part that you made hot.
Turn and twist the parts and it will come off without any damage on the frame.
Let it cool down just by air and wait until you can touch if with your hands.
Never use water to cool down because the stress in the metal will rise and damage or bend the frame.
The left over copper or silver can be taken off with some file strokes and sandpaper on a small piece of flat wood or on the file.
Never go to fast, take your time, it is impossible to put metal back on.
Only the rear derailleur eye must be taken of with a grinder or a saw.