Thanks for your help
Thanks all for your varying responses. I've finally been able to get down to the airfield since and do a W&B. with 2hrs of fuel + 45min reserve+SUTTO fuel, it looks like i can get everyone up and away within CofG and with 40lbs left over.
TODR & LDR are also both within available runway lengths, including for high temp, low wind and wet grass, so we're looking good.
I've spoken to a couple of the instructors there too who have said this isn't as experiemental a procedure as I had thought - just new PPL nerves i guess!