From the data I have both engines are the same power output. However there is a low compression version of both engines. The only difference between the 960 and the 961 is that the 961 was used in SE's SEL's and the 960 was used in SL's and SLC's. The only problem I see is if you replace a high compression version with a low compression version. This would not be likely if both engines came from the same country. The differences are most likely things like exhaust manifolds and airfilter housings etc.

117.960 177kw @ 4750 RPM 8.8:1 compression
117.960NV 165kw @ 4750 RPM 7.5:1 compression

117.961 177kw @ 4750 RPM 8.8:1 compression
117.961NV 165kw @ 4750 RPM 7.5:1 compression

Now you have the engine out and half appart. There was a 965 version available with 8:1, 9:1 and 10:1 compression. The 10:1 compression engine without a cat put out 195 kw at 5200 RPM. It probably also had a different set of cams. These parts might only be available in Germany??.

The data I have came from my 107 service CD

John Roncallo