This is a far from perfect answer, and ignores "I do not want to scale down the mesh and adjust in Blender." But it presents a method that should work reasonably well.
- There is a bug in the Blender DXF importer (0.9.6) created by the changes between Blender 2.79 and 2.8x. There is a simple fix, though. Edit the file do.py found in the addons folder. For example:
C:\Program Files\Blender Foundation\Blender 2.92\2.92\scripts\addons\io_import_dxf\dxfimport\do.py
Change line 1400 from:
bpy.context.screen.scene = scene
bpy.context.window.scene = scene
Import the .dxf file making sure to check the "Center geometry to scene" button in the merge options.
With all the elements selected press s to enter scale mode and then type 0.0254 to scale the objects to the exact size. This number is the conversion factor from inches, your DXF file default, to meters, Blender's internal default.
Note: I didn't use snapping to do the measurement so it's off a little bit.