Look here, you'll see the tarif per cc capacity. It might be different for something that age though, give the STVA (Strassenvekehrsamt = DVLA in the UK) a call, they're usually pretty helpful:
Detailed information on what?
How many priests and nuns can be squeezed in a car in Fribourg?
Or how much to tax a car in your area?
Here is a clue. Strassenvekehrsamt.
This user would like to thank dmarkd for this useful post: