Sibson is on 122.3, the same as Blackbushe.
Aim for the Morborne TV masts to the south, or Ferry Meadows lakes to the east (west side of Peterborough). National grid power lines track NE from the masts, then when they cross the A1 that's the extended centre line for 24 (25 in the old days). From the lakes it's pretty much on long finals.
Real pain to spot from the west, it hides behind the trees!
Para DZ is on the NW corner but remember skydivers take the wind into account so may be a mile or two upwind at altitude. All circuits to the south and east, no overhead join, no deadside.