I am actually running the 850J in the front and 863 in the rear with 30 mm spacers at all four corners, so I would recommend the J up front and running the 863 in the rear and maybe 30 mm spacers in the rear and 20 or smaller in the front so when your loaded it is level.
Also, you can run the BP shocks a little stiffer in the rear, doing so might change the handling characteristics of the LC. Stiffer springs, stiffer rebound/compression can cause over steer.
When I was road racing on sanctioned tracks I had the rear of my car higher and stiffer springs in the rear along with a 29 mm sway bar made for over-steer but I preferred that.