Thanks pawoSD, you set me on the right track with your 90 degree comment... Right after I posted my response to you I remembered where I had seen some of those L-shaped pivots like I'd described: in the locking mechanism in doors of my wagon. So I checked the 300SD and sure enough, it has them too!

I was able to use them to install the actuator at a 90 degree angle! It worked great. Photos forthcoming...

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)