Just for the record; My 6.0 AMG was converted late 1994 and the receipt dated 16.02.1995 says DM 41.650 (that included an alternator at DM 850)
It was not a complete 957 package though but engine & transmission upgrade and front brake upgrade (no E60 suspension, AMG muffler and 300kmh tacho upgrade). The front brake upgrade was mandatory by AMG for all 500E prior to 01/93 when getting the E60 engine conversion. The brake upgrade is no more than the late 320 mm discs and calipers coming with the facelift, or mid/late 1993.
I have a copy of the 1994 AMG price list in case someone is interested. BTW, the 300kmh AMG tacho upgrade P/N #C7 54 0002780 was DM 1020,75