Hi there,
You bought the right car for upgrades! [-/
There are exhausts, cams, heads, lightened flywheels, alloy fans alloy sumps, rocket covers bigger carbs fifth gears, but you need the one thing my wife won't let me have....and that is a budget to spend on it!

Check-out e bay and axel gertl, there are quite a few german websites mentioned on the forum.
Beware of the shiney bits
Mick (Bis13) was saying how the allow rocker cover is rubbish because the breather is smaller, but think he got around it by making it bigger. The alloy fan is not as efficient as the original and lightening flywheels etc brings out a can of worms of balancing but there are people who can balance it all up again.
Do it before you get the car on the road, as like me, you'll find you won't do a thing if the car is running.
Should have just told the wife I need a new head...crank...etc etc [-/