what is it worth....early A wagons

It's not so much the speed that may be the problem.
Picture yourself driving from the passenger side when you want to pull out to the left to pass a big rig on a two-lane road.
It's no longer an issue of pull out just a bit to see if traffic's coming. You'll have to have over half of your right-hand-drive car over in the opposing traffic lane before you'll be able to see what's about to run head-on into you.
I've got a Mopar buddy that lives in Oz and he's told me that this is a BIG problem when driving our left-hand-drive classic Mopars down under.


Just as driving with anything else, allow yourself the distance to see around.
Tailgating to where you can't have a full view around the offending slower driver and accelerating when you're in the other lane is a piss poor way to pass.

Stay far enough back, pick your break, and accelerate in your lane so you can get around and get back in your lane as quickly as possible.

So, you might have to stay a little further back, but if you're sticking your head out to see around him to begin with, you're already doing it wrong.