Nice R129. A 500SL 6.0 is very rare stateside.
Just a few bits of clarification:
-A cooperative agreement was concluded between AMG and Mercedes in 1990.
-The first car developed in collaboration between AMG and Mercedes was in 1993. It was a C36.
-There is no official record of the number of pre-merger AMG examples produced, let alone color combinations.
AMG was a la carte. Customers could order full body kits, AMG/OZ 3pc wheels, suspension packages, interior wood packages, etc. independent of the power plant options available at the time. The same goes for the performance modifications. A customer could order a M119 6.0 and choose not to make any exterior modifications. Until Mercedes began incorporating said performance options within their build sheets, the only way to prove providence is through an official work order from AMG or one of their officially endorsed outlets, engine work included. Otherwise, the only way to verify the engine displacement of any
example without documentation would be to measure.
There are a number of reproduced items available on the open market, some of which are in fact decals but the authentic AMG decals specifying engine modifications, spark plug specifications, etc are the same as those found on your example here.
But as you've pointed out, anyone could slap a decal and a badge under the hood and call it a "real" AMG.
Good luck with the sale.