1983 1.6 Diesel power hike?

I was wondering what the easiest conversion would be for this car, the 4 speed gearbox ratios are too long and the 1.6D is pretty pathetic by any stretch of the imagination.

The snag is this is my daily and I want to keep it diesel for economy issues… so what are my options and what is involved?

EDIT: Would this go in with minimum fuss: http://cgi.ebay.co.uk/1997-VOLKSWAGEN-GOLF-CL-TDI-GREEN-ESTATE-SPARES-REPAIRS_W0QQitemZ120547885287QQcmdZViewItemQQptZAutomobiles_UK?hash=item1c1136c0e7