Note that the drivers usually do not read the margins from the PPD files but have their own hard-coded margins (reading margins from the PPD would be much better for generic printer drivers, to get all printer-specific into the PPD). So it needs to be fixed in Gutenprint. Please report an upstream bug, as told already in comment #10.
In the meantime use a PostScript driver or another PCL driver (hpijs, pxlmono, ...).
Note that the drivers usually do not read the margins from the PPD files but have their own hard-coded margins (reading margins from the PPD would be much better for generic printer drivers, to get all printer-specific into the PPD). So it needs to be fixed in Gutenprint. Please report an upstream bug, as told already in comment #10.
In the meantime use a PostScript driver or another PCL driver (hpijs, pxlmono, ...).