DKW 1000 by Günter Welsch (from Mayen ) 1959 ?
It's already been established by nicanary that the base was Auto Union rather than DKW, and the 1000 is right so it's an Auto Union 1000 SP Special.
The builder's surname was indeed Welsch and he was from Mayen in Germany, although I had the build date as slightly later.
So all we need now is his correct forename (not Günter).
Still locked for SACO.