Hi Johnjo,
Take care before trying to the body off the Invader. 90% of the chassis tubes can be exposed for repair by removing the inner panels, to take the main bodyshell off needs all that to be done anyway, and is a lot more complicated! Suggest you join the club (if you haven't already)as there is plenty of advice available for you to mug up on. I have done both, so can speak from experience.