There most likely were specs for the toggle and likely they were not followed with much faith as there was a war on. I have found on many Brit plans allowance for local changes. Getting the job done seemed more important at this stage, and I think the Brits had finally learned this by DDay. But still, there were most likely specs. Try looking at Brit re-enactor sites for toggle ropes for an idea of what it should look like. I made one simply by using a belt sander to taper the toggle and cut the grove by hand.