1. Without apt-ftparchive

You don't need apt-ftparchive (1) (which is not available on a potato system) to make your custom package apt-gettable.

1.1. Create package overview files

apt-get (8) needs package overview files Packages.gz (for binary packages) and Sources.gz (for source package). To create them, use dpkg-scanpackages (8) (for Packages.gz) and dpkg-scansources (8) (for Sources.gz).

You need the following files to create them:

Put all the files in the same directory. Note that you don't need .changes file.

dpkg-scanpackages needs the override file. It is a text file for overriding the Priority: and Section: fields of the control file. It has the following format (one line for one package):
<package> <priority> <section> [<maintainerinfo>]
Each field is separated by a white space. <package> is the name of the package. Replace <priority> and <section> with the same values in the control file, and omit <maintainerinfo>. You can add comments by beginning them with # .

If you don't care the Priority: and Section: fields, you can use /dev/null as the override file. Run dpkg-scanpackages in this way:
$ dpkg-scanpackages . /dev/null | gzip -9c > Packages.gz
dpkg-scanpackages outputs the uncompressed overview files for binary packages ("Packages", not "Packages.gz") to standard output. Compress it with gzip (1). In this case the packages will be marked as Unclassified by dselect (8). If you want to specify the Priority: and Section: fields, replace /dev/null with the name of the real override file.

For source packages, use dpkg-scansources instead.
$ dpkg-scansources . /dev/null | gzip -9c > Sources.gz

1.2. Upload

Upload the packages, the files Packages.gz and Sources.gz in the same directory of your web server, say, http://your.web.server/debian-custom/ .

In the above example, the "apt lines" (the lines for /etc/apt/sources.list) are:
deb http://your.web.server/debian-custom/ ./
deb-src http://your.web.server/debian-custom/ ./
Note that the slash at the end of each line is necessary.