The advantage to drilling is the allen head will provide a center. Those setscrews may be hardened, making it, to say the least, much harder
I would drill as absolute last resort and try it somewhere you dont give a shit about. You can always helicoil in a new thread if you do have to drill out.
I would see if you can rent or buy an impact driver tool (hit with hammer and it turns very slightly). Not sure if they make allen bits for this though
When you replace use anti seize and see if you can order the setscrews from hollaender
Hey, if you want me to take a dump in a box and mark it "guaranteed", I will. I got spare time.