Hi, I did find Peak conventional, and it was easier to find than I expected.
Car is a Rolls-Royce Silver Shadow: they have aluminum blocks and heads, with wet liners. Some have claimed the OAT/HOAT chemicals attack the O-rings. Hard to know, when a car is 40 years old, if it was just at the end or if the coolant did it. I don't know what the O-rings were made of in 1970.
Anyway I did have the Mercedes-Benz coolant in it, which is Zerex G-05 I understand, and no problems after about 3 years, but it's drained now and to refill, I played it safe.