I have limited experience with this, but did get several LED drop-ins from Nite Ize that gave new life to some old Maglites. So, if you can find something from Nite Ize that looks like it will fit your lantern, you’ll probably be set.
However, unless you insist on continuing to use this particular lantern for sentimental reasons, I would suggest that a new LED lantern might be a better option. Some of today’s offerings have really useful features you won’t get from a drop-in LED module, such as multiple brightness settings, white and red light options, and battery level indication.