The duct from the passenger front wheel well can also be blocked by both critters and simply vegetative debris. Ask me how I know.....

How this engine WILL start with either the intake or exhaust open is pretty confusing. Your initial post indicated that you were more or less driving normally and then had to limp home while laying smoke which is what started this saga. Is it possible that running the engine caused something to get sucked into the intake tract-or pushed something down the exhaust-in either case preventing intake air or expelled exhaust from moving?

With the crossover removed, everything forward of the engine itself is removed as a choke point. The turbo just blows air into space but it still spins due to the exhaust moving down the pipe. If the crossover is in place and the cat removed, is it possible that, due to the boost which you are now getting, that air flow is at a much higher volume which allows sufficient air to make it through a potential blockage in the intake.

By the way, have you cleaned out the crossover tube? That impacts both incoming air and turbo boost.

As for the calls being screened: Click and Clack seemed to screen diesel calls pretty effectively since such calls were rare and they mostly did not know squat about diesels.

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87 300D 265Kmi
Factory rebuilt crate 603.96x engine at 200K