I think you would like a 15-90, or a 15-91 on a frame better. The harp size is similar. There's a reason that all of the LA, MA and SA systems that I've ever seen have a vertical bobbin. The quilt being on top of the bobbin's slide plate would be inconvenient to change and disruptive to the quilt.
As for a king, I think you'd find it incredibly tight. The take up bar will grow in size very quickly as you roll the quilt. By the time you rolled to the end, it would likely be about 3ish" per row. Size your pattern accordingly.
You can turn the quilt to "regain" some space for the last half, but your design still has to be very carefully chosen.