I have two heads in front of me, and one says 2.6, the other 3.0. There are certainly minor differences; even though rockers and camshaft are identical, valves are different.

The 2.8 is a (later) M104 engine - completely different. No way it could fit!!! Perhaps a 3.2 head would fit on a 2.8 but I wouldn't try it the other way around.

My two bits

Vivian

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1939 170 - till I was 3, still turns heads
1989 300TE - daily driver has 263k
1987 300E - purrs happily with 120k
1983 300SD - keeps my friend happy