I got a Palmetto Arms Dissy upper quite awhile back that I've been sitting on until I could make some mods. I finally got my A2 uppers and I'm trying to remove the barrel from the original flat top upper.  It came with a low profile gas block that has two set screws. One came loose without too much effort, but the other one is quite stubborn. I'm guessing some serious threadlocker is in play here and I don't want to strip out the hex set screw trying to get it loose.

I was thinking maybe heat is the answer, but the only options I can think of are my wife's (no pics) blow dryer or flame (lighter, torch, etc).

First, is heat the right answer? What other options for getting this stubborn thing off? Any other advice?

Yes heat...anyway you prefer. Then if you have messed up the socket, use a torx bit, if not use a hex bit and hammer in the shock and seat it and it will come out just fine.

How much heat is needed? Would a hair dryer suffice? Wife may have a heat gun for her crafting stuff.....

Likely more heat than a hairdryer puts out.

Hair dryer will work. Just hold it close. The set screw you have out, look down the hole as you do it for the loctite to start melting and it is ready then.

This.

All day.

lol, I use a hand torch myself. It is much faster. I used to use a heat gun but kept knocking it over and got tired of super gluing it back together.

Soldering Irons can also be used.