I dont think Ballroom Blitz was ever covered by 'BOC' (I cant find it anyways).
Sunny, not familiar with Sweet? We must get you acquainted then. I like Sweet a lot. They have some great tunes. 'Ballroom Blitz', 'Fox On The Run', 'Love Is Like Oxygen', and 'Little Willy' are some of their better known hits. I like 'White Mice', 'Stairway To The Stars', 'Burn On The Flame', etc,,,. They even did a cover of 'Paperback Writer' which aint bad. You should check them out.