just to go back to my earlier point about the nature of the climbs, what you need is 1100m of climb at a nice easy gradient, tarmac or gravel, the climbs are not technically hard.
The details to consider, i have done it and had the cycle computer tell me the temperature in Grimentz was 30 Celcius, i have also seen ice on the Croix de Coeur, it was the same year by the way. I have seen the race cancelled due to snow on the Pas de Lona.
The route is from 1500m up, depending on who you are altitude does matter, you might be able to find a climb but you won’t have the base altitude to work from.
You can not recreate the climbs in the UK, so don’t bother trying too hard.
Just ride, ride lots.