The downgrd.zip file you have requested: Modifications / Ultimate Doom v1.9 to Doom v1.1 Downgrade - 3.81mb is not available. Perhaps try browsing all files for the game Doom and upload any files you want to share or are missing. This is the only information we could locate:
Ultimate Doom v1.9 to Doom v1.1 Downgrade
This is a program written by Lee Killough (email@example.com) to downgrade
Ultimate Doom 1.9 to Doom v1.1. The purpose was to enable anyone wishing to
experiment with the network packet drivers Returns Doom v1.9 to Doom v1.1.