You'll have to use your 2.6 inlet manifold, air cleaner, and KE components. The 300E inlet manifold and air cleaner won't fit under the W201 hood.

The 2.6 inlet manifold runners are a bit smaller than the 3.0 as are the 2.6 head inlet ports, but this should not cause a problem.

I can't speak for every sensor, but most of the KE and other ancillary components were the same for both engines, so I think your integration problems will be minimal, but there were probably some year to year differences that you might have to deal with including A/C compressor, alternator, and PS pump.

The 3.0 head has larger valves and ports. I'm not sure if the exhaust manifolds are the same. If you use your 2.6 exhaust manifolds open up the entrance with a die grinder to match the 3.0 head if necessary. I'm not sure if the 3.0 exhaust manifolds have larger outlets, which may preclude bolting them to your existing 2.6 exhaust pipes.

Basically the 3.0 long block should "bolt-in" with minimum integration problems based on an "informal evaluation" I did some years ago on the possibility of converting my 2.6 to a 3.0, but I didn't pursue it beyond this stage. It might be down a few peak HP compared to a 300E due to the 190E 2.6' smaller inlet manifold runners and more restrictive exhaust, but it should definitely feel stronger.

Duke