I'll take you up on it. I weigh 192lb, goal of 1:59 for the full (but for now let's just say 3:45), VO2max is 50.0
So, first according to the calculator a VO2max of 50 is equivalent to a vVO2 of 9.68mph or a 6:20 pace. This means a desired goal of a 3:45 marathon pace (8:35) is 72.2% of your VO2max. Most marathon runners are somewhere between 60%-70% (for you 10:20 min/mile to 8:52 min/mile) but elite runners can take the percentage as high as 85%. So a 3:45 pace is towards the upper end of normal for your current fitness level, although it is definitely doable with good running economy/mechanics.
Over the entirety of the marathon you will burn an estimated 3682.5 kcals. Given your pace is 72.2% VO2max, it is estimated that 2474.6 kcals of the 3682.5 total calories burned will come from glucose. Assuming an average male leg muscle mass of 18.3kg (20% of your body weight), you have 1466.2 calories of glucose stored in your leg muscles. This means without tapping into any other source you will have a deficit of 1008.4 calories of glucose. The average person can take an additional 100 kcals of glucose from the liver without putting the body in danger, thus your final deficit total is 908.4 calories.
This means that either through a carb loading schedule prior to the race, or a nutrition plan during the race you need to consume an extra 908 calories to complete the marathon without hitting the wall at the pace you desire (3:45 marathon) given your current fitness level. This breaks down to 242.3 calories per hour if you decided to only use a nutrition plan during the race.
The other key is total carbohydrates in g weight. Purely based on your weight, you would need to consume between 61.1 and 87.3 carbohydrates per hour to push past the wall if you were to do no carbohydrate loading prior to the race. Research shows the human body limit is around 90g of carbohydrates in good conditions (not too hot or humid). So you're upper limit is on the threshold for the capability of the human body to consume that much without starting to cause GI issues. For every 2 g carbohydrates consumed you need to drink at least one ounce of water. Thus, for the duration of your marathon (3:45), you would need to consume 327.3 g carbohydrates and 163.7 ounces of water. If the conditions are worse (hot/humid), you may need to consume more water. Research has shown that consuming carbohydrates in two different forms increases the body's ability to absorb them. Thus, some combination of any two of glucose, fructose, sucrose, maltodrextin, etc. will allow the body to absorb a slightly higher amount than a single carbohydrate source.
Given all of this information, it would appear you would likely need to do some combination of a carb loading plan prior to the race and carb consumption during the race. Hope this helps and let me know if you have any other questions.