The logic/display board is almost a backpack (that is, 80x36 mm intended to mount behind 2x16 character LCD module), but it will cantilever off the two "short" ends by .6 inches. It will still fit that way onto the mounting pins for the i2c display module originally intended to mount on the lid.
You'll have to drill 4 new holes in the plastic interior mounting panel to accept the HV/relay board, but that should not pose any particular difficulty. In fact, you'll be able to use the mounting hardware that comes with the enclosure that's intended to mount the OpenEVSE board.
Like Chris' DIY 30A board, there are two PCB mounted relays on the board, so the overall amount of wiring is reduced. You just wire the HV path through the relays. The AC Power and AC Test wiring is taken care of by the board.