Have you given any thought to locating it below the upper trunk floor? Mine is a Mk 3 of course but unless the photo is decieving it appears your Mk 4 has at least that much room in the same area.The battery sits on that flat plate in the trunk.
I talked to Mike today and I bet your motor arrived today. He said he just got a 302 from Ford today that was on back order since January.No, just 302/340H.P. There apparently has been a bit of a backlog from Ford. It's OK though, at least it hasn't been taking up space in the garage.