There's an awful lot of play in the rear wheels when held and wiggled side-to-side. That's the only reason I suspect the bearings are worn. They don't squeek so they're probably not dry yet but I can't think of anything else that would cause such play.
I've been told that a slide hammer is the way to go but an alternative was to bash them out with a long drift from the opposite axle. I'm not sure whether this is a viable option or not and I'm also not sure whether there's a risk of damaging the diff. I just don't know what to expect until I get the drums off and have a proper look.
Apparantly you can buy a repair kit which includes bearings that sit further along the axle if mine are damaged. I suppose if a new axle (or two) is cheap enough that would be a better option.
Why would anyone design bearings to sit on the axle shaft and not in a cup of some sort ? I just wish I could visualise these bearings.
Thanks for the input chaps. Will let you know how I get on.
* edit - I just found this which looks very helpful and might be handy for others too.
http://www.thirdgen.org/techboard/transmissions-drivetrain/493071-tips-tricks-installing-axles.html