Here's a link to a guy's site who converted his 1974 450SL to megasquirt:
http://www.mercdjetmegasquirt.britautorepair.com/

Interesting reading...

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C