Welcome to Kent Scoobies
For geometry i would go to Elite http://www.elitedirect.com/ and speak to Barry, you'll also get a SIDC discount
ALK & uprated ARB's are a good mod and will also help reduce the understeer
Not many places in Kent but you could try Barrett's motorsport devision in Canterbury, quite a few of us use Xtreme http://www.xtremescoobies.ltd.uk/ who will also be able to do geometry soon (in about a months time hopefully), also Mocom http://www.mocomracing.com/ are getting a good reputation for there work