Sure Reggie,
That's possible.
Quite a few people did try conversions towards a more modern or more powerful power plant in the W113 chassis...
Personally I think a poor car waiting to be reanimated should hold for such a conversion and not a good survivor.
OK, what has been done in the past:
a) Conversion into a 220 Diesel
Walter Klatt did that. Just search the home page here for his diesel conversion of a 230 SL which is now a 220 SLD.
b) Mercedes M116 or M117 V8 transplants.
See Hatch & Son's hompage for two very nice and authentic conversions.
c) Christian Kromm (not on our site) has a small shop near Worms in Germany and did a perferct conversion to a 280 SL 6.3 with the M100 Grand Mercedes engine.
This car has even air suspension and is supposed to handle very nicely - in contrast to the unique 1967 factory prototype that was later destroyed ... :'( :'(
See "auto-kromm.de"s homepage.
d) Several (most extremely) ugly conversions with some US-V8s.
Mostly these cars' authenticity has been irreversibely destroyed.
Depends all how much you are thinking to do on your own...
Good luck
Achim
(prefers to stick to the originals)