The pack.png world converted from alpha to modern versions.
This is the pack.png world converted to 1.14.4+. It should load up with no problems on every Minecraft version after. Some of the original world has been generated a bit, but if you travel too far you will start to see new generation. There is a worldborder set for that purpose to keep you inside.
The seed is 3257840388504953787 and you can find the mountain at X:49 Z: 0
Generating the original world
To generate the original world, load up Minecraft Beta 1.3 and use the seed. Then save the world and close Minecraft. Open the world folder and delete all the region files. Then load the save in Minecraft Alpha 1.2.2 and you should see pack.png.