This seems like a lot of work for a small gain in performance. Isn't your 91 already a 3.0? It's basically the same engine as far as I know, (different bore X stroke). What are you trying to get here? Why not performance tune your current engine. ie induction, performance chip for ECU Better exhaust. All are relatively simple to accomplish. Benzmac, what do you think??
Good luck

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Jeff L
1987 300e
1989 300e