Congrats on the new tool, Mike. Just how many do you have now?...
A coupla things....
I suggest you drop out the TG and bolt, use a scrubber or something like the SLIP Cleaner to get the crud out and then lube with CLP or SLIP 2000. While it's out, clean out the receiver and wipe on, wipe off, with more CLP or 2000.
Since you changed the stock, I don't need to tell you to remove the stock and lube the back of the receiver and that fitting for the stock bolt.
Next, dismantle the forearm. Go over all the metal surfaces with an oily (CLPy?) rag, and put it back together. Be sure to lube the threads on the end of the action bar tube.
Next, remove everything from the mag tube, and clean it as if it were the bore, lubing lightly and then running a few clean patches through to reduce the lube to a thin coat.
My guess is the wear marks on the mag tube indicate a slight bend. If it functions fine, fuggedaboudit. A good smith can straighten it out PDQ if there's interference.
Also, some Expresses were made in the late 80s with standard gloss blue finish.
Sounds like a good "Using" shotgun, let's hear about how it shoots...