House Rules for TSR Gamma World 2nd Edition
from the introduction:
This is a bunch of stuff for a Gamma World game I ran 2010-2012 and was based on the second ed rules from TSR. I got my first copy on a trip to London at Hamley’s in about 1984. I still think it is one of the best Box set games ever. Art, layout and completeness it is one of best gming products ever. After this I had to choose between Gamma World or DnD so I started my Planet Psychon Setting a mix of both. I haven't touched it much and will need tweaking for your own game to work as it was ad hoc rather than really made to be a complete system.