My backs appear to be scrubbing on the outside a bit - make me suspect the cambers a bit out.

I'm wondering if Dudley's "individualising" might be worthwhile on the K3.

Could it be the tracking on the rear that is scrubbing your tyres rather than camber? Probably the easiest and cheapest of all the adjustments that you could check. (could be toeing in and scrubbing the outside edges, toeing out would scrub the inner edges if I remember correctly).

Believe me you would know if it was toeing out

A few years ago I parked next to a yellow K3 at Stoneleigh, it had MGF wheels, but had needed heavily modded black plastic wheel arches to clear them. It also had shock absorbers and/or anti-roll bars. I had a look underneath it with the owner, but can't remember all the details.