From what I can see, there are pretty much identical. I don't know if they share any components at all, but the 90 is descended from the 80 in many other parts. I don't like the fact that it's a single cable to one side that is then slaved off to the other wheel. I'd prefer two cables from the handbrake lever, through a balancer, then on to each wheel. The slaved, driver side is the one that tends to suffer more from wear and scrunge in the moving bits. Which is odd given that it's not the kerb side one that runs in the gutter. I tend to adjust the nearside one first and then the driver side. I might try doing it the other way around next time and see if it makes a difference, It shouldn't. On the bell crank there is a hole with a pin that goes through it. Any wear in those is magnified in movement in the lever inside the cabin. There is no bush in them. Just metal on metal. It is this slack that you are taking up when you adjust the little screws outside at the back of the drum. I am going to need some longer threads in a bit as I am running out of adjustment!
Chris