I'm not sure about this, but I think if you have a good R4 that fits and has the correct o-ring seal for use with the ridiculous manifold that is used to seal against the compressor, I can't imagine why not to use it.

One thing that I am curious about is that the one bolt that holds the manifold in place against the o-ring seals is a metric bolt. I don't know if this was done for Benz or what. If your compressor fits otherwise and takes an English bolt, be sure to use the bolt from the compressors application, not the metric one from the compressor that you remove, I would just investigate and be careful. If you strip this hole in the compressor, you will have problems and possibly have to toss the compressor.

Good luck,