Hello Terry,
Welcome to the Group.
As to your question,
replacing or repairing the interior is not the end of the world.
Most members here had to have some or more work done to their interior in the past.
Gladly you have got a Mercedes, and most materials (vinyl, leather, tufting or DB nylon-loop carpet) are still available from the usual sources (see vendors list). However, not all colors from the old days are still available and perhaps some of the new materials aren't _exactly_ the same look as the old 1970 qualities of materials were; often these are modern replacements (leather for instance) which come pretty close to the original.
A 2+2 California Coupé is not more complicated than a regular softtop-compartment SL. Everything in the interior is identical up to the drivers' seats; from behind there, the 2+2 are different. However, the material is identical.
Cave: If you plan to replace your factory-original MB tex (= MB vinyl) with genuine leather, the seaming of the rear bench is different as the leather-trimmed bench has more seams than the one covered with vinyl.
Why don't you just show a few pics, and we can perhaps guide you to more explicit help here.
Good luck!
Achim
(no California but ex Washington (WA) car)