I am able to use my LaserJet 6L with Windows 8.1 by using a Belkin USB-to-Parallel printer adapter ( I tried two other printer adapters that did not work). The Belkin version is a bit pricey but cheaper than a new printer:)
1. Go to Control Panel-Devices and Printers.
2. Click on "Add a Printer."
3. Click on "The printer that I want isn't listed."
4. For USB connection, choose "Add a local printer or network printer with manual settings."
5. Pick an existing port. I used the Belkin USB-to-Parallel printer adapter with an LPT port at one end and a USB at the other, so my choice is USB001 (Virtual printer port for USB).
6. Now you see the list for manufacturers and models. Before doing anything, click on "Windows Update" and let it run (takes a few minutes).
7. Once the update is complete and you are back to the list of manufacturers and models, select HP as the model and select HP LaserJet 6L as the printer. Without the Windows update, it will only show "HP laserJet 6L PS Class Driver", which causes the problem. Stick to "HP LaserJet 6L"
8. The rest is straight forward. Print a test page and check if it comes out right.