Doug, I know from talking to my Dad, and workigng next to my Grandad as a 4y.o. that they has 20s, 30s, 20W, and rarely 40s., which got changed around depending on season etc.
Then 20W-50 is one size fits all for decades.
Shell in the 80s had "Super SF" 20W-40, breaking the trend, then introduced Grey bottle XMO 15w30, which had a rep as an engine wrecker, apparently (was working in a Shell Garge at the time) due it it having a higher level of oil consumption than the average Aussie could deal with...Holden later had their issues with the 30s and oil consumption in the V-6 Commodore, and put in bigger sumps and longer dipsticks.
Then in the late 80s, STP and Penrite started the "thicker is better" 25W-60s, 25W-70s, 30W-70s, and even 40W (they made some of their rating up)...and I don't know why, but the majors started playing that game for protection "in the Aussie heat".
Personally, I don't see anything xW-50 in my future, and am happy with 5w30 in my L67, even 'though Holden in 1997 said 20W-50, and 15w40 in the cold.
However, I've heard the argument a number of times that Oz is thicker as there aren't thinner basestocks here.
Which made the NextGen, only available in 15w40, a grade not made in it's home market, a little interesting.