4th, I just recently built 2 Polish Underfolders too. One for myself and one for a buddy. Both of them had EXTREMELY tight upper handguards. I got the one off my buddy's gas tube after about 1/2 an hour. Mine took about 2 hours spread over about 3 days. I finally got it though. Then I shaved it down in the right spots to make it go back on easier. It's still stiff, but workable. The way I finally got it off of the gas tube was to wrap a soft rag around it, and as gently as possible squeeze it in the vise from the sides with the bottom facing up. Then turned the gas tube with a 12" adjustable wrench. It still took awhile, and I'm kinda suprised that I didn't crack the wood, but it came off without any damage.
You did a good job on those 2. They look great. My buddy's turned out perfect, but I messed up 2 front trunnion rivets on mine. I was driving the barrel pin back out because I had borrowed one from an M70 kit while I was waiting for a new one to come in, and was swapping them out. I really need to pull the barrel and replace them, but I've been lazy.