Will a Pre-He V12 XJS need an unleaded conversion?

[TWINTURBODAVE]

Hi, as the title, I am looking at buying a 1978 V12 XJS. The owner reckons it will need some tuning to run on unleaded ( it hasnr been run for 15 years). Is this the case? And what does it require? I know some other cars require hardened valve seats etc??

[a8hex]

The head is alloy so it would always have had hardened valve set inserts. The main market was the US and they went unleaded years before we did.
Not sure about the compression ratio and whether you'd need to do something about the octane rating, but I don't think that was an issue for the V12s, was 5Star available then?