L4D2 Animation Editing and Porting

[agent1138]

Hi, so I have a little idea what I have to do but I need some pointers.

I am trying to make a mini mod for L4D2. This will change the speed of the zombies to slow like old school.

Getting the zombies to walk slow is easy, however the animations stay static. Is there a feasible way to:

Slow down the original running zombie animations so they would appear to be walking,
replace all running animations with the shuffling animations to match the new speed
Or import some other slow zombie animation from say hl2 or another source mod.

Preferably the ideal option would be to use the original walking animation and just replace the running one, but I can't seem to find the folder they're in.

Any help would be much appreciated.