On the brake test machine my MG1100 came up with left and right differential of 72% on the rear brakes.
Not good, although I couldn't tell in day to day driving. A panic stop in the wet may have been interesting.
The work shop manual says I need service tools 18G-304 and 18G-304B
to get the drums off.
Can I do it without them? Any advice for a first timer?

Ok..I've had look at it and I will need some kind of puller.
Also the left side rear hub assembly was about to fall right off
One of the three bolts is completely missing, one was very loose and one can not be tightened.
Also they seem to be fitted back to front...that is the head of the bolt on the outside. As best as I can tell the diagram in the manual seems to show the nuts to the outside...can anyone confirm which way the bolts should face?
Also which way should the dish in the big washer face?

You don't need a puller, you just need to get creative. Just back the wheel nuts off a bit and use the wheel as a slide hammer. (It takes a bit of technique but they usually come off fairly easily. But don't undo the nuts too far and stuff the threads!)
Don't forget that the left hand hub nut is a left hand thread.

The three bolts only hold the backing plate to the trailing arm. They do not hold the hub on. It does not really matter which way the bolts face (as long as the nuts are at the back!)

Big washer? Dish?

is it a different setup to a mini?

The Hub and drum are one piece.

It's easy to make a puller. Piece of flat bar between two wheel studs and a bolt through the middle to push on the stub.

_________________

Hey, I just had a thought.*

If you have the spare wheel retainer clamp in the boot you can turn that into a very simple hub puller.
You need to get a nut that fits the retainer screw and than you bolt the retainer to the hub using the wheel, turn the screw and the hub falls off.

*actually it was more of a recollection of a long forgotten memory than a thought but this was a tip given on the ADO16 mailing list a long time ago.

Actually that is very clever.
I did try the slide hammer technique but after nearly dislodging the car off the stand...Thought it better to make a puller,
a bit of flat with 3 holes. Still surprisingly tight.
Every thing was in excellent condition just the backing plate bolts missing or loose.
This car had a complete restoration probably 10 years ago but there seems to be a lot of loose nuts and bolts all over it. Just hope there's none in the engine.