I wouldn't call the older diesels "sooo slow", but surely they're not for everyone, especially for the performance-minded individuals. The main reason older diesels aren't as peppy as the newer ones is that many of them are naturally-aspirated, i.e. no turbo. There were some that did have turbos. Look for an 82-85 300D or 300SD for example. The 87 300D was the most powerful passenger car diesel of its time. The secondary reason why the newer diesels are more powerful is their direct, electronic, high-pressure fuel injection. I think taking an old diesel and modifying it is a waste of time and potentially a costly project. I'd just get a newer diesel if performance is your primary objective.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL