They aren't height adjustable as far as i know, only adjustable damping. Your springs will determine the ride height. more info here http://www.kyb.com.au/performance.htm
seriously by the time you buy spring and shocks, your close to coilover money. just get coilovers, set the dampening to the softest setting and it'll be fine. my tein HA's were on medium height softest setting and it was just as comfy as stock suspension even though it was slammed.
i can only reccomend the tein HA's as thats what i used, don't know the kg rating either. got em second hand for $600 from tekky few years ago
Have a ponder on Yahoo Japan and get them shipped through Streeter... just recently got some slightly used ZEAL Endless Function Xs coilovers for $740! Z32 Tein HA 8k/6k used 14000kms going for less than $500 - http://page2.auctions.yahoo.co.jp/jp/auction/b113710100 then there's Z32 Top Line Aragosta Type-S 9k/7k brand new going for over $3000 - http://page19.auctions.yahoo.co.jp/jp/auction/x146416721 Shipping is another ~$250 on top with Streeter.
Here are the ones I went with, TT which is the street version with 8 & 6 spring rates, Got them from Otomoto in Sydney, They sell for $1399 I was lucky enough to get them a bit cheaper thru a friend. I'm not planning to track the car just wanted full adjustability height & ride for street use. http://www.otomoto.com.au/HDSystems/ttseries.htm
sweet im very undecided as to coilovers or not i can get the KYB GR2s shipped for 116.45 not sure if its US or not and 210.39 for all 4 shocks... decisions to make...