Thanks James - I have found a couple of Mercedes ball joints parts that look very similar - I'll post info if I come up with anything... as it happens, I live only 3 miles from Mulfab so will also ask there...

1983 + 8
1978 + 8 DHC
1959 + 4 DHC
1959 + 4
1953 + 4 Interim
1953 + 4 flatty
1952 +4 flatty DHC