Regarding the advice below:
"Also at this time before you go further I would cut the shoulder hoop (between the front rollbar and the foward seat uprite) and install the inner (sleave) tubing support, Now is the time even tho you might not need it now for the spec, it might happen later or you might go up in class or sell the chassie to sombody else."
Current copy of 2.4C seems to agree with the edition you posted the diagram from. I'm a little confused as to the necessity of the interior reinforcement tube as you described.
If I'm reading the spec correctly, the "upper frame rail" is defined as beginning 2" forward of the rear motor plate upright, and extending rearward to the vicintity of the rear end upright and the forward seat upright, at which "shoulder hoop" begins to exist, with step-up maybe required if the two entities are not one and the same, (the larger seat hoop tubing at 1-1/2 x .058).
This would seem to allow the upper frame rail / shoulder hoop to exist as one piece, as it appears to be on PalliP's car, or to consist of as many as many as 4 individual pieces, butt-spliced and sleeved as many as 3 places.
So I don't see why you would want to put a splice there if it's already one continuous piece meeting the spec in the case of the shoulder hoop, and exceeding it in the case of the upper frame rails???
Is there maybe some more advanced spec that would require the splice there
Thanks for any insight,
John Williams