right, I am now home so can type this up a bit better.
The original g-4B lacing panel from the suit is as follows (thanks to merliner for the pictures and the measurments)
Panel is 2" across. the tape is 3/8" wide. each loop is 3/8" (ie the same material) and 1/4" of loop. (this means each loop is a total of 1.2" long before being folded over.) The gap between each loop is 3/8".
I got 6m (yes 6m) of ribbon from a haberdashery, 1/2m of grey fabric and a bottle of fabric glue and some dark green thread. The laces came from a cobblers but are a bit of a light green. Can't dye them because they're polyester but they'll do until I find something darker.
Size 8 RAF jacket. Measured 1" down from the top of the sleeve, (that's the top of the patch), the patch is 3" high, so I then measured 3" down, that got me my approximate starting point for the laces panel. From there to the velcro at the base of the sleeve is 22.5" (bear in mind this a size 8, so I expect sleeve length to vary)
I cut out a panel of grey material , 25" x 3", allowing 2" clear at the top of the panel and 1" either side of the laces. The idea being to fold over the sides underneath. The top piece will go under the patch to help keep the whole thing intergrated. Examination of the screencaps of the jackets seem to me that they go under the patch on the arm.
Then it was just a matter of creating the loops, (25 per side), gluing them to the tape,then gluing the whole ribbong of tape and loops to the fabric panel. As you can see in my photo I then laced them up to make sure the laces were long enough.
When you consider it is a 1.8m lace, there wasn't much left at the bottom.
This weekend I am stitching the ribbon to the fabric. Ironing it (the instructions on the glue say it bonds better with heat) then stitching the panel to each arm. (pictures to follow once done)