Chassis no. GRS30 - 010624
Production date not known, first registered 23 June 76
OK, so it's a 2+2 model. The springs are different than those on a contemporary 2-seater.
There are two possibilities I'd suggest, as the factory service manual gives data for 'Standard' and 'Hard' suspension type on this model, market and the likely production date.
'Standard' is probably more likely for your car, but you should be able to compare the data with what you see on your car, and make an informed decision. Active turns of coil should tell you the difference:
'Standard'
Active turns of coil: 8.5
Free length mm (in): 381 (15.00)
Spring constant kg/mm: 2.06 (115.4)
'Hard Suspension'
Active turns of coil: 7.5
Free length mm (in): 341.5 (13.44)
Spring constant kg/mm: 2.59 (145.0)
Edit to add: Note that these are for FRONT springs only.