The Brother HL2040 driver that comes with Puppy uses the built-in Ghostscript hl1250 driver. That's why it doesn't require any additional software. You can see the PPD file in /usr/share/ppd.
I believe that it is based on PCL, because I can install my Brother HL2070N as an HP Laserjet 6 and it works fine.
You can see the complete list of internal Ghostscript drivers with the command "gs -h". Any printer that works with one of these drivers can be installed just by getting its PPD file from openprinting.org.
For the sake of comparison, you can try the official Brother HL2170W driver from here.