ok so i want to build a kit car. i have a 3.6 litre (226) 4 speed automatic from an '88 Jag xj-s. i need four seats, it needs a rigid chassis. what materials should i use for the chassis and is tubes better or square pipe? what thickness should it be. the car will be about 17 feet long. and just out of interest, do i need catalysts on the engine? (i am in the UK) and are ther any weight regulations?