Give Any Robinson Race Cars a call, He will be able to sell you a full copy of the 25.4 regs for about £35. You will need a full set as the floor design changes dependent on how the rest of the chassis is being done.
Thanks Jim, will do.
Speaking with Mark Norton a while back and he said that full tube frame cars completed from 2013 onwards will need to have a floor spec to comply with 25.4, so whilst I'm still flexible on the floor, I wanted to get it right now to save re-doing stuff down the line.
I found this on the net which gives a reasonable handle on the bar position for the floor on the centre left diagram, but it's always nice to touch and hold an original copy.