I have been speaking to them on the phone for a while now, the bloke told me that if you have air bag suspension on leaf springs they will not even consider to insure you. Coil springs are fine. He said that is the only modification that will throw you out instantly.
They seem like they know what they are talking about, because my accesories are twice the market value of the vehicle they have to contact the underwriter first but he reckons it will be fine.