I think the tdi conversion(or any engine conversion) is cool regardless if it's an 8 yo xj or a 24 yo(we're all xj lovers here). Even if it costs you $2K when all is said and done, if you ever wanted to sell just the engine, you'd get at least $1K, and I'm sure there's a VW or diesel head out there that would be willing to pay top dollar for an XJ with a TDI.