Are you guys going to Hereford Sunday? I am going to be there, I'd be happy to look over your cars and give you some pointers
0 tranny height will give you less forward traction but more side bite, this combined with the other parts of the 'Ellis UK' setup works perfectly, I would strongly recomend you copy the 'Ellis UK' setup down to the very last detail and your car will be dialled.
Weight, minimum I run mine is 1670g, maximum 1800g.
If grip is high and the track is flat then I find you can run the car light, otherwise the car is better around 1720-1750g