Intrestingly in 1978 against Poland in the opening game of that World Cup he was played as a CB; in a line of Vogts Russmann Kaltz Zimmermann.
The English commentators pointed out how the Germans were despreately missing Beckenbauer's presence - as he would normally push into MF shifting the entire team formation up and into attack. The display was very laid back and defensive, "un-German...negative" the colour commentator gave, highlighting in how Russmann sometimes tried to move pass the half way line but was highly ineffective, while Kaltz attempted to rain balls around from the back but was incapable of crafting anything remotely dangerous - him getting himself in to spots of bother when he tried to dribble/ground pass the ball out of defence lead to the commentary off, 'Kaltz is a good defender as long as he does not think too much'.
He did just bomb it to Tomaszewski or on rare occasion Germany sent someone up, the ball was gobbled up by Zmuda/Gorgon. I was actually more impressed with Zmuda on the ball than Kaltz - the Pole went for at least two decent dribbling runs and laid three quality passes for the forwards - astonishing and here I thought the Pole was shit as a footballer...to be fair to Kaltz on the LPasses from the back, Germany played a 4-5-1 with barely any options upfront.
As a CB he was okay, nothing outstanding - the 'casual' display prompted a shuffling for the rest of the tournament, to (RB)Vogts Russmann Dietz Kaltz -- thus he played as leftback, maybe Side to both?