As with all things a lot would depend on how much your willings to spend as once you've attacked the shell its starts to get very expensive, you could loose a good 25kg by ditching the anvil in the front and using an alloy version of the block.

Using rally/race spec parts will also help reduce the weight, a TR30R turbo for example only weighs 12lbs but is rather expensive. WRC calipers are nice and light, magnesium wheels, diff casings etc also help to reduce weight. Areoquip have the startlite range and using silver wire instead of copper allows for a thinner lighter loom, but in all seriousness unless you have a race team budget it would probably be easier to just start with a lighter ford like a mk1 escort
After that
Find a set of magnesium wheels, some WRC calipers as these only weight around 2kgs instead of thetend to be 1kg lessll depened onAll depends on hows