In option 2, you use the same front fan.
It means making a special shroud, one that will redirect the flow from horizontal to vertical. It isn't preferred, but it will work.
You really don't have a million options here. I knew you were after some performance, so I can only really see the bottom mounted heatercore working for you. What's left is how to fit the fan(s).
You could mount a lit/colored fan in the side panel, to assist the front fan, as described above. Mounted correctly, it shouldn't hinder the operation of the door. I happen to know that you're capable of doing this
. It would certainly be unique!
Alternatively, you could try to get creative with that long VW(?, ref HC DB) heatercore, but I just can't picture how it'd fit.