Hi gonzo,
My last 70 miler was 3 weeks ago. We set off after a breakfast of bacon, scrambled eggs with cream and cheese, mushrooms, and tea with a little milk. 3 units of Humalog. You have to match insulin to protein intake just as you do for carb intake, only the ratios tend to be different.
Many health professionals only discuss carb/insulin ratios, but insulin is still required to deal with the glucose metabolised from dietary protein. Another common myth is that carbs are somehow essential for exercise, but ther's no truth in that one.
Low carb is perfectly do-able as a vegetarian although protein sources are going to be more limited.
All the best,
fergus