Use a roll pin punch for the pins. If you don't have those, get a drill bit the same diameter as the pin, chuck it backwards in a drill press and press them out.
Replace the quad seal if you're getting new seals anyway. That is one that often leaks and you'll just need to do it later. On the poly tube, I countersink a very slight depression in the breech to accept the tubing. It will stick right in there while you assemble the tube portion. I use Oxpho cold blue - works good.
"but I'll be needin' that gun, fer squirrels and such."