W460 1981 Upgrade?

 Hi,

I have a W460 GE280 1981 that drives, is in medium condition for it's age, but poor condition by modern standards.  I am considering being silly and upgrading the whole thing with a turbo diesel engine, body repair / upgrade and complete interior refit.  I know it sounds crazy, but I am trying to persuade myself that it is a sensible thing to do.  It might not be quite as crazy as you would think, because I live in Ireland and I would only have to pay £40 road tax and £50 insurance plus no MOT required.  A job of this scale is outside my ability.

(1) Is it a stupid idea?
(2) Where should I get the work done (I assume GB)?
(3) Any idea how much it might cost?
(4) Any other fool out there done this before and want to share their woes?

Thanks,