How did I ever miss this site? Never mind, that is NOT my "one question"...

We are the owners of a '91 420SEL, our first Mercedes. 120K miles, just performed the 60K major service, everything is just wonderfull! What a car!

As to the question:

Are there any sources/options available out there vis-a-vis replacement short or long-block PERFORMANCE ENGINE upgrades for this 4.2 motor? I keep reading about Mahle pistons, other camshafts, various AMG modifications, etc. This historically all seems to be directed towards the 5.0 and 5.6 motors. I'm not having any problems with my car but plan to keep it for as long as possible (it really is just broken in) and am the kind of person who tries to do the advance research & planning as far in advance as possible. I recognize this is not the same as finding a long block for a 350 Chevy or 302 Ford...

Thanks in advance for your consideration!