Completely De-older the two base pins required for function (always check the base diagram first) before soldering in leads going into the glass envelope or bulb. Or at least de-solder enough that you can see through the pins. This is traditionally done by hams with a baseball wrist-flick quickly after melting old solder in a ham's messy workshop with backstop cardboard or with a fast downward rap, etc.
. If your experienced, fast and watch your lips and scatter area you can even blow out the melted solder.
I think the original base was cemented to the bulb with glyptol cement when original.
Just using an epoxy or gorilla, tm. glue should be ok if your choice can stand operating Temperature. Be careful not to break the original bulb base seal extension in center of socket.
Then after glue is set, solder the leads making sure adequate solder is wicked up into proper pins.