There is indeed a bug with setting custom paper sizes in inches. It is improved but not yet ironed out completely in the recent 2.2.0 rc version. You can try this file made with it, for scale 1:1:
inches_34_22.dxfDon't try to edit the paper size settings as it seems it gets ruined then. If you want a different printing scale, scale up the frame accordingly (x600?) or delete it.
You could also just use ARCH D instead, 24x36, a bit larger.