Instead of ruining yet another MB engine, how about using some penetrating oil, some patience, and an external bolt extractor? Drive it down over the head of the allen bolts and they'll either come out or snap off. If you used penetrating oil and waited, they should come right out, they're not that tight to begin with.

Why does the intake manifold even have to come off? If it's that crusty and crappy, leave it. Remove the injector hard lines and go at the glow plug wiring from the sides. You can get in there with a long extension and some patience. Key word: PATIENCE.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)