K-BXMOR1 is a Weldable Mortise Gate Box
The unit that you want to use would be the Keedex K-BXMOR4 Universal Mortise Gate Box, Centered, No Trim Hole, No Cylinder Hole, 14 Guage Steel, Suitable for Marks Mortise Locks, 1 ea as seen here:
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as it gives you only the mortise edge preparation and then from that point you will drill the simple function holes required.