Firstly good luck, I did a similar thing in 2008, 54miles in 24hours The Caledonian Challenge. Team Blisterin’ Hot Babes. (see what we did there)
Hope the training is going well. I think the longest one we did was 30miles (where we got hopelessly lost but thats another story).
Things that helped us:
amazing support team with a VW camper van:).
well used boots. dunno what terrain you are on, we were on WHW so boots were only thing i considered.
if its the same sort of set up with several checkpoints plan out what hot meals you will be having at your stops. Bacon and egg butties and hot tea at 3am made my morning! have plenty of nice treats for yourself for along the way, you will deserve them.
fresh baselayer/tshirt and socks when you stop. (more if weather is rotten) Separate change clothes into individual bags, so no hunting about for them when you are tired.
sort any feet issues when they happen
walking poles made life a bit easier, i used a pair of cycling gloves with mine
We treated it as a normal hill walk day out, so will all the usual kit we carried ibuprofen and paracetomol (just in case) and in my case knee supports.
if there are massage pit stops on the way, take advantage of them. They do help.
follow the bum shaped rock rule, if theres a rock big enough for your bum you are permitted to sit on it.
stick with your team.
i cant think of anything else off hand, questions welcome. have a good time, and enjoy, its hard but doable. :)