Long Brew Mash

[confused]

I'm planning my first "two corny" length of my stock strong ale this weekend. It may push my mash tun to the limits - what do you think

I have the 32l H&G mash tun which says it should handle grain bills up to 10 kg, mine is just short of that at 21lbs. I'm planning to collect 50l for the boil so by my calculations an initial mash of 25l should yield 15 after take up and dead space, so I would need to sparge 35l. Does that sound realistic, its a bigger ratio of sparge to mash than I am used to.

18lbs MO
2lbs crystal
1lb torrified wheat

1.5oz First Gold 90min
1.5oz Challenger 60min
1.5oz Fuggles 10min
1.0oz EKG Dry Hopped

Nottingham

Mash 25l at 67c 75 mins