4 way Wylexes are typical 70s kit, and were widely installed in the 80s as well. Those old Wylexes arent as old as they first appear. In the 70s they were partly wooden, and many people have misjudged their age.
ha, I hope so! If the leccy were added _sfter_ the gas there would be more reason to worry :)
Local earth rod, which you probably have in the form of an incoming metal water mains pipe. Confirming low R doesnt mean all is well, but it at least would eliminate the biggest possible risk of all, the lack of any functional earth.
Unfortunately having an earth connection doesnt automatically imply it will work as a safety feature. If earth R is too high, with no RCD the fuse wires would sit there forever more before anything blows, with the whole earth circuit live - but its not very likely to be anything like that bad.
NT