[harryf]

I have heard very good things about the aftermarket 'gripper' LSD's available from several of the UK specialists and I believe they are available to fit non LSD diffs and cars with the narrower splined axles.

Its the next item on my upgrade list if nothing else pops up to swallow the budget.

They are not cheap, but I don't know how much you're paying for the californian rear end so it may be viable, particularly if you save work and the benefits are of interest.

You would probably need to be an enthusiastic driver to make full use of one but they are apparently very long life and much more effective. If you trackday the car I have heard of the standard diff friction plates being considered as consumables needing frequent replacement.