Got this sorted in the end, just wanted to say thanks to all for the advice
She's quiet as a mouse now and the brakes feel a lot better.
I managed to get hold of a small bar of high strength steel from work to use as a drift, spent a while flattening out the corners of the plate (probably much to the annoyance of my neighbours) to get to the bolts. Used the same drift but backwards through the bolt holes in the backing plate to tap the axles out and the culprit was revealed

- Yup, that's broken...
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Got a friend with a garage to press off the old bearings and put on the new, he even gave me a hand getting the thing back together so was nice and quick and easy. Also good to have him there to bleed the brakes with me.
I am however curious about my drums...
They're not flat inside (which every other drum I've ever seen is), but it's not wear, they're machined like that

is this standard on the samurais???

- Grooved drums???
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And next on the job list... just got myself some freewheeling hubs of the bay... are they a straightforward enough job? Any advice or tips before I try getting them on?