Um... based on 3 hours of research which only produced 1 useful result, I have come to the conclusion that my '83 240GL/B23E engine can run on ultra-premium 98 octane fuel(called Optimax, Vortex and suchlike in Australia), without any lead-replacement-type additives.

I think I read right.

Am I wrong?

I have a 1981 244DL, with a B21A. I use BP Ultimate 98, but prefer Mobil Synergy 8000 Premium, as the car runs better . . . otherwise it pings. The Mobil seems better. Shell, Caltex, Woolies, Liberty Premiums, are piss weak! I have never seen any reference to using leaded, except in my 1977 B21E. Volvo does not specify, in any of my Owner Manual materials.

Octane is completely unrelated to the lubricating properties of lead. Your car can use regular fuel and still need lead for valve seat lubrication. Almost every modern car post-1970 is engineered with valves and seats that no longer require lead in the fuel and I suspect yours is similar. In the US, leaded fuel is banned and many old Volvos from the 1970s soldier on with hundreds of thousands of miles, unaffected. So I would use regular fuel and ignore the additives.