The way it works best is to take the power train and engine and stick it in another car. Not the Fiesta, unless you have it registered as a diesel, because of emissions testing. Find a fitting body that was originally a diesel, and stick your new power train and engine in that.

On the other hand, that's a lot of work... the VW Jetta TDI is probably cheaper.

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'79 300SD
'82 Chevy Chevette diesel