The turbo is only accessible from above or below the engine, not from the wheel well.

There's no benefit to using the MAP sensor line for the wastegate boost signal. You should be able to thread a new line from the ALDA area to the engine vacuum pump in the factory sheath, then cross into the sheath that goes to the emissions devices then to the wastegate actuator. Or fabricate a boost signal source at the mixing pipe.

Whether or not you remove the EGR valve, fabricate a metal disk to fit over the port in the exhaust manifold that the EGR standpipe attaches to. Use the collar clamp to hold the disk (and standpipe if you keep it) in place. In the future, you can attach an EGT sensor to this port You only need a gasket on the mixing pipe side of the blocking plate. If you see soot building at the seam, the EGR valve is leaking despite your efforts to disable it. An alternative to the disk is a freeze plug that'll fit in the manifold EGR port. That's what I did in an '87 300D -



Note the brass plug in the trap oxidizer style manifold EGR port. I couldn't find a freeze plug that was a good fit for the mixing pipe. Plus the mixing pipe is aluminum and I wasn't sure it would put with a pressed interference fit.

Sixto
MB-less