Why is a Max HR of 200 outrageous for someone age 51? I know a couple of very fit over 50's with 200+ Max HR. At the same time I also know a couple of very fit over 50's who can barely get their HR above 150, even when flat out.
The conclusion - age related Max HR are as Cougie says...bobbins.
The carbo load thing still leaves me flabbergasted too. We've had conversations about carbo loading in the shop many times in the last couple of weeks and they look at me like I've told them to fly to Mars. It's amazing how ingrained it is in runners.
FP - when I've gone into marathon not particularly well trained I start with 2:1 and then reduce to 1:1 when I need to. At your pace it won't make much difference to your overall finish time but it will make it a much more pleasant experience.
Stop and stretch the IT band before you need to and carry on doing it regularly.