"Custom springs" werent they "cut" springs mate ?
anyway, whatever you do to normal springs you fook them royally up - the ride will be crap and the actual structure of the spring will be damaged - which may actually throw you off into a ditch when the spring lets loose...
Dont do anything apart from pay "proper money" for a LOOOOOW coilover kit, fred paid loads for his, but his are ace, yes the drive is a bit rougher then normal, but I sh*t you not its a go-kart! nothing gets close to his for handling.