ok sunny's are easy,stanza stuff bolts in easy.almost the same floorpan.
struts :- stanza struts with girlock calipers will bolt in to the sunny balljoint.what insert?go to a motorcycle shop & get some 20w30 fork oil & use that in the with the stock insert,that'll make it nice & stiff.
diff :- again stanza,japanese is best,but a borg warner diff if you have to.
lower control arm:- don't worry bout this,get a pair of 200b steering arms,they're offset outwards,will give you extra camber.you just need to get 180b outer tie rod ends to match the taper in the arm.you could also just redrill the crossmember.as for castor arms,i don't know of any,you might want to grab some stanza castor arms to check.
springs :- go through a wrecker with a tape measure & try & get some springs with a heavier guage & close to the length of the stock ones.try something common,maybe gemini or some of the ke corolla's,just make sure they're the right diameter.
good luck with the hunt,& let us know what you do.

paul
p.s. leigh,please fill in the details on your signin,it helps us to know what sort of answers to give you.hope all the above helps.