@ Goldfinger, you might contact ACO or the ciruit at LeMans, the classics race held there surely use 4 star.

Also may be worth trying a classic car group in FR as they may be of assistance.

Rus

Welcome Goldfinger! Wont be out at LM this year you will have a great time!

BTW how did the gold champagne cork look?

Mr Goldfinger,
I'm intrigued by your post. I'm not a Merc expert by any means but I'd swear my b*llocks are cauliflowers if you don't have hardened valve seats in a 1981 car - my car is 20 years older than that, and hardened seats were standard even then. If that's the case then all you need to do is take it along to a rolling road and get a nice man to reset the timing for you, you will then be able to run it on standard fuel. If you want to wear a belt and braces then you could also put an additive in with the fuel as well, as has been suggested (my personal choice is Millers) and get a nice octane boost, but it wouldn't really be necessary and it can get expensive.
H

Your going to need to get the top end done for unleaded, wherever you go im sorry to say