Does anyone know just how much extra height the kombi box puts into a buggy compared to a stock beetle gearbox.?

Also the other thing was curios as to what people are using for making roll cages I have been advised to use 42 mm OD, 36 ID (3mm wall thickness), piping for the main cage.

cheers

How do you mean "extra height" ? You can jack up an IRS higher than a swingaxle safely due to the fact that the wheels stay straight. But a kombi box wont change that from a beetle IRS box. You will probably have to fit a lift kit to clear a kombi box.

Do not use pipe for roll cages, only steel tubing.
According to the baja bugs and buggies book, use at least 1 1/2" OD tubing, with a min wall thickness of 0.095" which is 13 guage.

36 ID is pretty close to a inch and a half,... it will be a buggy getting jammed around the scrubb a fair but so i want a fairly substancial pipe / tubing to take the impact and still be able to drive home. little extra weight not such a concern. Also i can get my hands on a mazada adaption plate to fit a rotary onto the stock VW box.
has anyone had much sucess with a rotary on a VW box before?
cheers