Would it be a good idea to use balljoints (the same you use on the front top wishbones) in the rear (IRS) suspension, so you can do the necessary adjustments (toe-in, camber, etc.), instead of using rose-joints?

They seem longer lasting, being all sealed up, etc. And they're also pretty cheap (5 quid a piece).

Any sound advice?

I imagine the difficulty is getting a suitable taper machined for the track rod end to fit into. Rose joints only require a normal high tensile nut and bolt.

There are other problems too - M18 Fine is not the world most common thread, and they're probably not that strong either, although GTM does use something similar on the back of their libra, so who knows. You can add boots to rose joints if you so wish, but bear in mind, as with all other seals, they keep bad stuff in just as effectively as they keep it out.

Kingr

Another problem is that regular ball joints (like track rod ends I assume you mean) are inherently offset, which I would not have thought was ideal for the rear links.

Unless I've misunderstood....which is entirely possible...