power steering pump

I own a 1975 Mercedes 450SL which needs a new power steering pump. I purchased one at a junk yard but they do not appear to be the same when placed side-by-side.

First, the original pump pulley is 6" in diameter and the junk yard pump is 5 1/2". Further, the original pump operates on a 2-belt pulley and the junk yard pump operates on only one. I would like to know if the junk yard pump can be installed on my 450 SL without problems. Please advise.

The specs on the junk yard pump are as follows: ZAHNRADFABNK FREDRICHSHAFEN AG.
Type Nr: 7672900404
Fabr. Nr: 542700 1.79
1164601780 65 br.

The specs on the original pump are as follows:
VICKERS TYPE 21
Fabr. Nr. 75 405245 Max Druck 65 bars