I must be missing something, nuts and bolts on a 606 manifold? If you sheared the head off the bolt why couldn't you pull the manifold and then use vicegrips on the threaded shaft left behind. If there's still some 'head' left on the bolt can you drill/cut it off and then pull the Manifold?

You can swap out the SOV leaving the manifold in place by moving the washer bottle out the way. Not as roomy as with the manifold out, but can be done. Please be careful of the torx bolts on the SOV....I stripped one of them over a year ago, which has delayed my SOV replacement for a long while.

It was a PITA to get that bolt out of the SOV. I finally figured out to drill the head slightly larger/deeper than the speed out's diameter I bought from the Orange Box.

Clean the torx bolts with brushes and brake cleaner so you get a great grip on it with the T27. Those bolts are not made of very strong metal and who knows how badly they maybe over torqued from prior service.

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Treetops
06 E320 CDI 127K Miles
87 300TD 231K Miles

99 E300 269K Miles-Sold