I've been ruminating on your desire to keep the bench. Maybe you have already given up on it, but I keep thinking about it. Then I tripped over an add for a Lokar shifter that incorporates an electronic rooster comb for shifting electronic transmissions like the 6L80E and it sparked an idea for. And no, they don't show anything for an 8HP.
What if you left the column shift mechanism in place and mounted the floor shifter for the 8HP someplace remotely and shifted it using a cable off the column shift arm? You would have to remove the detents in the 8HP shifter and wouldn't have access to the +/- shifting but maybe it would work?
Just an idea.