Johnny, Greetings from NZ.
Hope you haven't started the job of replacing the missing A/C compressor bolt.
I was cleaning around the underside of my 190E and noticed that one A/C compressor mounting bolt was missing. When I attempted to take another one out to measure it's dimensions, it snapped off without any effort! So instead of 4 bolts, I now had 2 holding the compressor in place. The upshot of this tale is that the MB dealer also broke one of the remaining bolts off. (Not their fault, in my opinion, just over-tightened bolts sometime in the past.) The A/C system had to be de-gassed, the compressor removed, and the bolt holes drilled out and rethreaded. Of course the system had to be re-gassed with R134 to complete the job. $600 later I got my car back on the road.
My advice, providing I'm not too late, is to leave the compressor bolted in place with three bolts. It won't go anywhere, nor cause any operational problems. Good luck!