Well we attempted the same last year and are re attempting this year.
Last year in the drier months on good trials we trained with Michelin dry xc’s and they were fantastic, but then the rain came and to be honest the only tyre that was anything less than lethal was panaracer trail rakers. However they are very skittery on the harder packed chalk with the green slime top coat.
Basically no tyre is a fit and forget, in drier conditions and firm I’d go with a dry conditions small blocked tyre with a tough casing(flint) in wet I’d look for something that clears easy but with shorter spikes as unless its proper damp they’ll deflect and you’ll be off and on your arse in a split second.
In fact if its been raining or starts raining heavy bin it, It was the most miserable 60 miles I’ve ever ridden, and the chaps that did complete took 21hours to go one way (including 2 broken ribs, 4 sets of pads destroyed and one person refusing to eat and drink anymore)