This may be a starting point:
http://www.peachparts.com/shopforum/showthread.php?threadid=1289&highlight=sportline+amg
I suspect that since there is an 'old' AMG logo, rather like an Alfa crest, that maybe the 5 blocks were a transitional thing while AMG wasn't quite part of MB, but was doing close collaboration. I sent a letter to the factory in Germany, got an email saying basically - we will get back to you - and never heard anything more. It sure looks like the Sportline badge evolved into the AMG!
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John
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E