Greg, thank you time and your excellent response - I will indeed check the shocks, shackles and bushings - and centrepins. One last question which comes to mind: I realize the illustrations are stock - and not specific to the liteace - but they do show an antiroll bar between the springs at the back. My van doesn't have one - and I'm wondering if it would be possible to fit an antiroll bar to a leaf sprung liteace.
Greg, that's great, I'll check everything you've suggested. The only diagram I could find rear end/ leaf springs was in the 'rear axle and suspension' pdf here: http://www.toyotavans.org/community/tips/toyo_manual.html
and (just as my liteace) there's no sway bar indicated - so yes, I'll look into getting a custom bar fitted.
Finally just to say many thanks advice - you've been a great help. Best Regards,