I'm not convinced you'll get very far with this - but if you can measure the length of the spring as it is now and make some rough measurements of the angle of the spring relative to the lower conrol arm (LCA) and the angle between the upper spring mount and where the LCA meets the chassis you should be able to get a rough idea of how much rubber you need.

I'd do this for you but the measurements on my W123 probably won't help.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!