Personally I think the civilian tracking is unneeded.
If zombies win and control the territory they get 2 zombies per IPC rating of the territory to reflect the civilian population being infected/taken. Yes that does mean that some of the bigger territories will hurt, Japan for example would generate 16 zombies if it fell. Though makes sense as generally higher IPC rating indicates a higher number of population. Make use of the originating IPC value of a country in the case of US or others that get income boosts.
Then reduce the combats losses to just 1 for 1. Tank, mech, etc, all end up being 1 zombie.
There are three types of models available from the Zombies!!! game. I suggest the following rules/stats for them
Regular Zombies: Attack 2, Defense 1, Move 1 (Can engage air units with ‘Zombie Pathogen’)
Zombie Babes: Attack 1, Defense 2, Move 1 (Can move across water at Movement 2 and engage navel units)
Zombie Dogs: Attack 1, Defense 1, Move 2 (Can blitzkreig like tanks)
All are equal in cost, IE you get to place 4 zombies, it can be any combination of the above.
Also remove the zombies random movement and make it more interesting. Have each player roll a d6 on the zombie phase, the highest rolling player gets to play the zombies. Attacks if possible must be made, IE can’t just keep the zombies standing at your border and not attack just because its you, but if you have more than one option you pick. Non-combat doesn’t follow this as zombies like to shuffle around mindlessly when not attacking.