If the barrel has been cut down to 16" then the gas port should be .118", not the stock .098. Pull the front sight pin and gauge the port to figure out what size the port is drilled.
As for the chamber, polish it out to get it to shine. The stock surplus barrel/chamber may have gotten a little rough sitting in storage for so long.
On the mags, clean them and check the spring to make sure that they are not going south. Also, load two rounds and press down on the back of the case. The rounds should pop back up cleanly to the top of the feed lips. If they don’t IM me and I will tell you the tweak to save the mag springs.
Pull the butt stock and the recoil springs and give them and the inside of the tube a good cleaning/lube. It may be that the tube is full of Parkerizing flakes that need to be cleaned out. I just use a brush on a few rods and give it a good spin down the tube to make sure the inside of the tube is slick and clean, then chase it with a patch. To get the springs back in the tube, use a rod (straighten hanger) to guide the springs back down, but the tool works better if you have one.
As for lubing the bolt/carrier/ receiver, use grease, not light oil. Don’t forget to get the carrier hood/channels greased too. The gas piston should be left dry, it will self clean, and lube just attracts more fouling.