Ah-ha! Success! I was able to drill the remains of the bolt out of the front wishbone using various sizes of drill bit and then, when only the thinnest of slivers of bolt remained on one side, drive a small screwdriver down and ‘peel’ the remains of the bolt off the inside of the hole. Job done! Voila:

 

Not wanting to stop there I figured out the only way the rear discs were going to come off was to butcher the splash plates and put a three legged puller on. So, I butchered the splash plates, put the hub nuts back on and popped the pullers on.

The first disc (where the adjuster had been accessible and the handbrake shoes backed off) slid off fairly easily; the second (where the adjuster had been inaccessible) came off with one hell of a bang.. still, they’re off now, I may just need new splash plates – but then these are pretty rusty, anyway:

 

Now I just have to break the rest of the rear subframe down into it’s component parts and I really am ready for refurbishing!