Why not keep it outside? My cat is an outside cat - only comes inside when it is real ugly out. He gets minimal care - good feed and minimum vet care like deworming and shots. They have street smarts and usually survive traffic and predators just fine. It beats not adopting it. This also would help with your monster indoor cats.
G
PS: My cat was feral and survivd several moves, even cross country just fine. Going on 13+ years and the LA foothill coyotes haven't caught him either.