A replacement MB block or engine won't have a number by the IP. It should have a tag at the aft end of the block on the turbo side below the block heater. IIRC the 7th and 8th digits tell you if it was a replacement short block (no head), long block or complete engine. Here's a sample tag from gsxr's collection:







I don't know how Metric and other rebuilders identify reworked 603s.

If you don't mind the work of replacing the engine, don't dismiss an iffy 3.5. You can swap in a 3.0 block for little more than the cost of a good short block and a head gasket. Under $1000 bare bones to $2500 if you succumb to while you're in there's. Don't make a decision without pulling the head to measure piston protrusion to confirm bent rods. A bad head gasket oil seal will cause symptoms of a bent #1 rod.

Sixto
87 300D

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Do you know what the very last 2 numbers Mean? On the CRATE motor tag???

One person- recently told me - that number identifies what was replaced with Crate motor??? Which confuses me... cuz- I assumed the ENTIRE motor was replaced/NEW???

Any one know?

Typically a "crate" engine is the short block and rotating assembly when we're talking about warranty or recall work. Block, bearings, rods, crank, pistons. Covers, accessories, and head(s) are usually transferred from the existing block unless not serviceable.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)