If you want to convert your Quik Check DOS specs to be usable in Quik Check for Windows, you have to open the DOS spec in the Windows specification designer. DOS specs have a file name that starts with QC#, where Windows spec file names start with QC$. Note that DOS specs are not lost; the QC# file will still be there. Make sure that you save the converted file as a new name, and under the File | Specification Options menu, change the title to something more descriptive that you will recognize, as this name will be what appears in the drop down box when you print checks.

As for custom page sizes (dot matrix printer?), you must edit the specification to be a custom page size. Do this also from File | Specification Options from within the spec designer. Also note that you will have to set up your printer to form feed 7" rather than 11" so that the Windows program can page eject properly with the character-based Dot matrix printer. You may also want to set up a custom printer driver for this and make this the default check printing option (from File | Options).