Have you tried to heat the gas block/tube to see if that will loosen it? My guess is that you have a little bit of carbon buildup. Heat may or may not work, but its something to try if you already haven't.
On the taper pin, I found that a heavier hammer with the proper support will usually knock the pin loose. Oddly enough I was helping a friend this morning with building an upper and the taper pins on the Colt FSB were in there pretty good. Used a large punch top get them moving with a heavy hammer with the barrel resting on a Wheeler AR-15 Bench Block (
https://www.midwayusa.com/product/1016339811) resting on concrete floor. One pin gave in fairly easily the other was a super PITA. Got it out though. It helps having a second person to hold the barrel in place so it doesn't shift.
Good luck!
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