Pros:

Great Job!
Awesome Port!
These could work great as zombie replacements
Maybe turn the Fast Zombie into the Hunter and the Poison Headcrab into the tank or boomer.
Maybe Zombine for Riot Zombies

Cons:

None that I can see, the mods does exactly as it states replace zombies with Headcrab Zombies
Could maybe fix the headcrab on the fast zombie

Conclusion:

I suggest also replacing the sounds to for added immersion!

EXCELLENT JOB