Looking at buying some harnesses but they specify harness bars for fitting.What are they and is it possible to use original seat belt mounting holes(inc rears for shoulder straps)?

Yes it is possible to use existing seat belt holes on some of the harnessess, the 3 and 4 point ones do

Ive just borrowed a 3 point harness for Trax tomorrow, then Im going to buy some :)

Cheers:).For the 5/6 point ones,do you bolt the crotch straps to the front seat mountings?

Not too sure about the 5/6 point ones, not seen how those get bolted

http://www.ravensblade-impreza.com site has instructions for fitting a 4 point one