You really don’t need that bastard big and ugly 70’s display stuck awkwardly on your bars. Use internal wireless module and you can have all that on your Garmin anyway.
P.S. Amey will try and build you the bike he wants if you entrust him to shopping lists
Not even looked into the junction box things. Will need to research this.
Did see XT Di2 SC-MT800 System Information Display which looks interesting.
Second shifter won't be in use in this case.