If the cam was installed 180 off, you would not be turning the engine. The vales would hit.

If you did a valve job, and for some reason, why I don't know, turned the engine over while the head was off, the pump is off. It is going to be much less work to just set the engine to TDC, remove the IP, align the marks on the IP, replace the IP gasket and grease both sides so it does not tear when timing the IP. Reinstall the IP and use the low pressure (drip) method to retime the IP. Remember to do two things when timing:
1) Remove all vacuum lines to IP, and make sure the IP is at FULL THROTTLE (and of coarse the cam lobes are "up")
2) Set the IP at 24-23.5 if you have not replaced the chain. If you have replaced the chain, set the pump at 25. When the chain stretches, it retards the timing, i.e., when you loose much power due to IP pump off timing, time to put a chain in .

If the camshaft was 180 degrees off, there would be no problem whatsoever with the valve timing. (The crankshaft being 180 degrees off would be different.)

To illustrate, let's say the the #1 piston is at TDC on the compression stroke. The head is removed, the camshaft is rotated 180 degrees, then the head is reinstalled. The #1 piston is now at TDC on the exhaust stroke. Valve timing is correct. The injection timing is 180 degrees retarded.

Sure about that?

Go put an intrusion engine on tdc, and set the cam 180 off, then crank it, you tell me what will happen

And yeah, I am sure about that, seeing as though I have been specializing in Benz for the last 15 years

TF is correct.

There will be no interference with the valves if the camshaft is set 180 degrees off the "correct" position. The valves will open and close on the compression/power strokes instead of the exhaust/intake strokes.

The only thing that defines the strokes is the injection event. Without injection, the camshaft can operate the valves in either of two positions..............0 degrees and 180 degrees.

You correct theres no interference ,but to turn camshaft you have to remove cam tower just 1st one , on the camshaft rotate spacer with mark 180 degrees and then rotate camshaft -- till align with mark,about 10 minutes of work.Without taking cam towers off impossible to turn camshaft,valves will hit piston.

Agreed.

I believe the appropriate term is "interference engine."

Did you say 15 years?

Ooops, I guess my thoughts where faster than my fingers.

Set to TDC to make sure timing marks are correct, but when installing IP set to 23.5-25 BTDC, depending on how old the chain is.