FWIW I don’t use those magwell blocks. I’m not advocating what I do, just passing it along.
I put the lower on my bench flat on it’s side with the ejection port side facing down. I then clamp it down to the bench with a quick grip clamp, and try to line that up with a spot on the lower where the aluminum goes all the way through. This allows the lower to resist the torque as I loosen the nut or the tube itself.
I’m assuming it’s the castle nut that is giving you the problem? Did you unstake the receiver end plate? If it is staked really well, it can be a real bear to get the castle nut off, no amount of WD40 will help. BTW, WD40 is a horrible choice for penetrating oil IMO. Use Kroil or PB Blaster to loosen nuts. Make sure you test the finish in an inconspicuous spot if you use PB Blaster, it can dissolve certain plastics and paint.
hmm… i have not removed an assload of A2s in my time- but as i recall, i think i’ve always just been able to hand twist off. is your buffer retention detent sitting in a notch on the receiver extension, perhaps?
i cant imagine grant would have loctited it, rifle REs really dont need to be in there all that tight… the stock screw locks everything down. you might want to contact him, though… if it’s loctite, you can hit it with a propane torch and burn it up.