I've been wondering this myself.

I have a NA 190 2.5 with a (probably) dead Automatic Transmission.

I've been quoted $3000 Canadian for a rebuild tranny. For that money, I'd like to put in a 5 speed, and I was thinking, hey, while I'm at it, I'd see if a turbo engine was available as well.

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MB 1986 190D in my past
MB 1987 300E on the street
MB 1994 'Smoke Silver' E420 in my driveway
1999 Mazda Miata in the fun stable
1964 E-Type Jaguar Coupe- Sold
1970 E-Type Jaguar Coupe- Sold
1968 Corvair Monza Conv. with Turbo Transplant- Sold
1986 Merkur Xr4ti- abandoned
various mundane American autos

If I'd known then what I know now...

Hell, I'd probably still have done it anyways.