the lower bush has a shoulder which aligns with the hole in the hub and a circlip secures it - thus, there is a definate poisition for it. the top bush however seems to have no clip or shoulders so is it just fitted centrally in the hub's hole and thats it, relying on interference fit so that the hub dosen't move on the bush under load?

the toe control arm doesn't seem to have any adjustment, is that just 'fit and be happy'?

Yes, the top bush is just held central only via an interference fit.

The Toe-Control arm has no adjustment at the knuckle (outer end). However it does have a cam arrangement (like the top bush bolt) to adjust toe-in at the sub-frame end.
If it's anything like the pair I've just replaced on ours, the bolt will be siezed in metal bush centre & the nut rusted solid on the bolt thread.
I had to cut the bolt at both ends with a reciprocating saw to remove the arm. Paul,
2001 Discovery 2 TD5, 211,000 miles & climbing
2006 FFRR TDV8 Vogue 151,000 miles & now sold
Member of Midland (Land) Rover Owners Club, www.mroc.co.uk