someone suggested the Alfa V6 as it is light, powerful and very cheap. I have been looking and it should fit and even comes in FWD guise in the 164 & 166. The wheelbase of the 164 is 2660mm and the 166 2720mm so a little longer than the Mk3 at 2474mm.
This is a terrible idea.
What do you want to do, spend your term in Germany trying to make something work, or driving?
You'll be in Germany, with a Brit registered car on German-specific insurance, cooked up by the British forces.
You need something simple, reliable and fun, which can be battered around a long race-track endlessly.

The letters A, B and F are coming to mind very readily.
Alternatively you could look at a 1.8T, but it's far more complex and heavier. You will also use more consumables.
Spend the money on the cage, buckets and harnesses, then an ABF and 02A 'box and then an LSD in the 'box, then ITBs for the ABF.
This should keep you busy and entertained for some time.
Oh and don't go thinking parts are cheaper in Germany!