I doubt it. The two blocks have different coring. Both have the same stroke, but the 3.0 has a larger bore and they are siamezed - no coolant between the bores. The 2.6 has a full cooling jacket around the bores.

Heads are different with the 2.6 having smaller valves and ports. Too bad Mercedes didn't increase displacement by just varying stroke on the same long block like Chevies, but Mercedes never seems to do anything the easy way.

Duke