I'm sure Ken the Guru could give us the absolute answer on this, but it's my understanding that the strengthening was added to the vehicle in production sometime in late '56, but the earlier cars were never recalled to have it fitted. Certainly there are plenty of '56 FEs getting about today without it.
In a more general sense, I don't think the idea of Safety Recalls became prevalent in Australia until the 70s. They were a by-product of Ralph Nader's campaign in the US re the Corvair: "Unsafe at Any Speed" and all that. Was the HQ the first car to suffer a limited recall? I have an idea it was - I think I read that in "Heart of the Lion" - but as always, I stand to be corrected....
cheers
RET