First, welcome on the forum!
The steering servo is just a servo, no special things to it.
There are different sizes, you will need the standard size servo, used in 1:10th scale cars, 1:8th scale cars, helis etc.
The servo you linked ( s1903MG ) is not strong enough for the steering.
You can use other brands to, like Savox, Hitec etc.
If you want to keep an Ace servo, the DS1015 should be a good one.
So any standard size servo with more then about 15kg should be fine.


I hope it helps!

Ruud