01:33 Jun 19, 2009 

Land after the war was handed out to ex service men in forty acre lots, it was considered a good size of land from which to make a living from. I grew up on 20,000 acres, and we had paddocks called the north forty, the southern 100, west 50 and eastern long, when we talked about where the cattle were we always knew where each of us was talking about.
But:
roaring 20's = the years 1920 - 1929.
roaring 40's = winter winds (40klm)
Southern 50 = car race (50 lap/mile race)
Highland 50 = Scottish Pipe band with 50 members / 50 hectare lot of land in the highlands
As you can see it is a phrase which can be made to suit any occasion, and generally a small amount of research in the follow up text will give some clues to the answer.