Best upgrade possible is to fit a larger engine

I recommend fitting a 1.6 x-flow with electronic ignition and a mild road performance cam and twin 40 dcoe webber carbs

It will cost too much to get power from the 1.3

For any engine work I recommend a friend of mine Wayne at WPE ( wacky performance engines) he built a friend of mines 187bhp x-flow

For any more questions don't hesitate to ask bud, I used to have a aspirated cosworth powered mk2 a few yrs ago and miss it like I lost a limb