Plotinus... The Alpha Zombie is what started it all and are, as I see them, from "regular people" who became the Initial Zombies. That said, the Alpha Zombie would be best as a "Super Normal" type because lets say they have more Virus and are more Powerful and or evolved from the initial Virus and longer term development. A sort of Fresh and Powerful dose of the Virus made them not only what started it all but more powerful.
This means they could look like what you have there but would have "Civilian Clothing" and Blue/Grey Skin Tones. I think it is more than ok to have them be a little larger than the Other Zombies with the exception of the Monster Zombies. There are many ways the Looks can go so there is "Artistic License" for that...They simply represent what started it all and I think are more powerful due to the Fresh Powerful Dose of Virus as well as having been around longer to evolve stronger but without so much Mutation. Probably worn clothes or tears here and there.
...Are you considering making this Unit? IF so.....
This means they could look like what you have there but would have "Civilian Clothing" and Blue/Grey Skin Tones. I think it is more than ok to have them be a little larger than the Other Zombies with the exception of the Monster Zombies. There are many ways the Looks can go so there is "Artistic License" for that...They simply represent what started it all and I think are more powerful due to the Fresh Powerful Dose of Virus as well as having been around longer to evolve stronger but without so much Mutation. Probably worn clothes or tears here and there.
...Are you considering making this Unit? IF so.....

Perhaps some Skin textures in livid color could be placed if you have a fast way. If a Gown is too much trouble, he would be fine without a shirt...then if you can add some skin textures to sort of make him have that "yes, I am the Alpha Zombie who went through it all from the start" type thing...that would also be a nice added touch.

if possible an enlarged version (minus the gown) could be used as our Monster Zombie: two units for the price of one?