It should be DIN but with copper nickel you should be fine imo.

Bloke I work with, 30 years in the trade makes brilliant shaped brake pipes, I was watching him making them and he used SAE for them all, I asked him and he said he always had done them all like that.

I still use DIN for DIN fittings, he still does them his way, neither of us has had any bother, we do use a decent flaring tool though, that could make a difference.