mcdat, It would be very difficult to move the chassis rails and have it passed as safe. Manufacturers spend a lot of time and wreck a lot of vehicles to be sure that the design is ideal. I would need to see the car and the design plans. What is the goal/reason for moving the rails?

steveo, The legalities of a conversion like this can be simple or complex depending on the year model of your car and what ADRs it needs to comply with. It is definitely passable. Obviously there would need to be upgrades to the brake system etc. Price will vary car to car. Give me a call for more info.

Cheers