Shimano Dura-Ace Di2 internal wiring kits are designed to work only on frames intended to support Di2 internal wiring. Please don't hesitate to call with any questions regarding Di2 internal wiring. Questions we will ask will be regarding the location of the battery and juction box.
The EW7975-A-1 and EW7975-A-2 have both internalize all wires and the junction box and work with a Di2 specific short battery mount. The EW7975-A-1 kit has a 400mm wire to the battery for batteries mounted under the left chainstay or under the bottom bracket. The EW7975-A-2 kit has a longer 1010mm wire for battery placement under the saddle. The EW-7973-2 kit internalized all wires, has a short battery mount with the junction box mounted externally typically where the BB cable guide is usually located.