Some explanations seem to be necessary here.
The card edge connector is weighted down by any attached PCB, regardless if the PCB stands up or lays flat. In both cases a support is required, and without a support the connector is weighted even more, when the PCB lays flat, than when it stands up vertically. The PBI connector has intentionally and on purpose been mounted like that on the interface. The reasons which led to such decision are these:
1) reduction of the place occupied by the interface. It seems important for many people.
2) straight card edge connectors are much easier to buy, than right-angle connectors (not to mention straddle-mount connectors)
3) in any case the problem of some support must be taken into consideration. The PBI connector mounted this way serves as a support for the PCB, when the interface is inserted into an XE computer, so this way it per se solves a half of the support problem.
It should be taken into account, that it is not possible to make an universal support for the same PCB to be positioned flat behind an XE and XL model, because the neccesary distance between interface and the desk surface with XE is different than with XL. The interface is designed so that one can attach it to an XE, and, after a while, to an 800XL without much trouble. The interface, as it is, when connected to an 800XL, rests with the PCB's surface on the computer's chassis. What remains to be done, it is to add suitable support so that the PCB is tightened and the connection safe. For example as on the photo below (it is only a provisional solution, please don't pay attention to the fact that it doesn't look very aesthetic at the moment).
As to the ribbon cable connection, as I wrote before, it is possible to use one, if the disk sat upside down, and a right-angle header installed on the component side of the PCB. But I wrote that it was not recommended and there are some reasons to say so. Ironically, I spent few past evenings investigating, why single words are regularly lost in I/O with certain computer (while not with any other one), and finally I found out, that the reason is a too long cable, which was interfering with the internal operation of the machine, and that, in turn, influenced the interface's operation. It is possible that Slor used a long cable to connect an IDEa to PBI without problems, but in this case it is not a good idea. The hard disk's FIFO is very sensitive to any glitches leading to data loss, especially if there are power lines nearby, where fast and significant current changes occur, e.g. when the disk is moving the heads (esp. if the current goes through several tiny wires from a power supply which is common to the entire setup). It will not necessarily cause instant problems, but you have been warned.
The basic concept of powering the interface, for ergonomic reasons, provides no separate power supply. In 800XL, where there is no 5V on the PBI, it should be added using short, thick wires from the motherboard connected to the same pins, where the 5V is in the 600XL. For those, who cannot do this, or do not want to modify the computer, the final version
of the PCB will be equipped with a separate power connector. Anyone who insists to connect the computer using a ribbon cable also should use the separate power supply.