this may not be relevant to your question........but.............
If you are already at this stage of the chassis build I,d strongly suggest you make all of CP16 out of 3mm steel
It makes it very strong ( pedal box attaches to it ), & also if you use 1.6mm steel when you come to weld it to the chassis you can bet your bottom dollar it will distort/bellow , this won,t weaken it but as this is also where the steering column support bush is located its better to have a more rigid plate
just a little thought for you
cheers
andy