Weidner...I would definitely like to meet you. You have the most deliciously devious mind. Out of the box completely...
Nath...to take care of the eye, try using the lines of your living room ceiling. Take your shotgun & set a stance in the center of the room....mount the shotgun & swing along the lines of the wall to ceiling while disregarding the front post.................try it and adjust your gun/mount positions to produce an even a swing as possible. Slight wobbles won't matter. Oh yes....both eyes open........
The key to negating an opposite eye dominance is to focus solely on the target & forget the front bead, using it only to adjust the gun/mount initially in your practice. Focus on the target & let you subconcsience (sp?) do it's job. Fitting a stock is expensive & not really nec.
Don't use American skeet sustained lead methods...listen to Mr. Churchill (shotgunner, not politician). Swing through only.
Two things to add...the 870 is my fav. & I have shot fine English, Italian, German & Russian shotguns in competition & the field. You are an American shotgunner in essence & adjust too quickly to be fitted as you adapt to the configuration in an instant.
PM me for any further discussion.
By the way...the London shooting school have the best instructors in the world...and so is the school.
LB