Sounds like you've got it covered. IDEALLY they should be the same body, so the controls are where you are used to them. The other thing, is the cameras hanging on straps and banging around, as you walk through the crowds. A friend, holding the extra lens would help, other than a second body. Also, at events like this, a good photo vest can be your camera bag and not worry about putting it down and then it walks away!
Like a wedding, just have a list, ahead of time of the "must have " shots and you or your assistant, can cross them off, as you get them. So in this case, shots of people signing in, warming up, jogging,etc. is good and then the "must have" shot of the beginning of the race,starting line and hopefully the eventual winner in the front, which I would use the longer lens, so when the gun goes off, you can get out of the way,
Rich