Go slow, avoid wedging a screwdriver in the seam, make sure you have all bolts and screws removed.
I use a length of wood dowel and a light hammer and tap gently around the circumference and LIGHTLY on the crank until the joint splits. The 850 has roller bearings, so this will not impede the separation.
I personally don't recommend the pullers that Old Britts sell as I am concerned that too much pressure can warp the cases or strip the threads for the primary case.
YMMV