Is rear chassis rails conversion necessary?
 

I have built the chassis to the book specs. I have not modified the rear rails area though. The difference to the book specs is that instead of 20mm diameter dircular tube i have uses 20x20 rectangular tubes joined with angles at the corners. Look at the attached pictures to understand.
I am a bit reluctant to cut these rails as i think that they offer some bit of extra stifness to the rear part of the chassis.
From your experience, do you think it will be possible to install the SSC rear GRP panel to my chassis? Thanks!

In a word, No it won't fit and you would be better off waiting till you have what ever rear panel you intend to use then fabricate the frame work to suit.

I was planning to powdercoat my chassis prior buying the bodywork. But you are right, i should get the rear panel fitst. Thanks!

The ssc rear panel has more of an angle at the back than the book and uses a frame at bottom I believe you can find the correct measurements and placements for these tubes on here somewhere just do a search or ask spud69

Hope this helps