The CNCC guide is normally pretty good, so if you're not familliar with the rigging I wouldn't try to skimp out on rope lengths. That said I would normally use a 50m rope for Lancaster Hole, which is fine the way I rig it, but you have loads of options with the rigging in there now!
If you don't have a long enough rope, you could always put in a knot pass, or just be prepared to get most of the way down then come back up, just don't forget to put in a good stopper knot in the end if you're not sure it will reach!
Alternatively, if you don't have enough rope, why not go in one of the many other entrances that don't need so much, if any rigging?