I have a SS-CJBF 85 blank I want to set up for 40# jig/bait with a 870 two-speed and am looking at cork tape with shrink wrap over it. Is there any rule of thumb for reel placement, like elbow to wrist or palm measurement for end of rod to reel center?

I measure elbow to palm so it can tuck underneath my pits and still give me a good winding angle for the fighting fish. If you have a fighting belt then i think you should sorten it to elbow to wrist, so the winding is with more power. Its more personal preference.

tuck the butt of rod under your arm and grab hold or the rod with your hand, get it.

Elbow to palm is the way most will rig + or - 3dB.