Lastly, but the most important question: What kind of changes would you employ, if any?
That's all entirely up to you - not a directly helpful reply, but it's an approach that will make life a lot easier for you down the road.
The rules are not particularly prescriptive, and the armoury and marketplace are totally incomplete rules-wise, so make up something that sounds close enough.
If it turns out to be too strong, too weak, or doing something different to what you want, just change them mid-game and don't tell anyone - if you're the GM, they probably won't notice, and if they do you can tell them it's a Machine Spirit glitch.
For the Servitor's armour, you could make a fair argument for Carapace (Av4-5) on the left arm, chest and abdomen, and Flak (Av3) or cloth (Av1-2) elsewhere based on that model photo. The same is true for most of the 40K models pictured (lots of Carapace, some cloth).
Or to make running the game easier for you to focus on the more interesting characters (i.e. the ones operating a complete brain), call it Av3 all over and leave it.
Flak-Gown can just be Av2-3 on those you think would wear protective clothing - soldiers, forge workers etc - but maybe skip it on those that shouldn't be in the line of fire like the squat.
Lights? I don't know if they have rules, but just let them ignore darkness in the direction they are facing for visual-based stuff (spotting, shooting, etc.).
Maybe they can blind people with the glare when nearby (target passes an Initiative test or suffers a -20% to sight-based stuff).
I don't know if Leader fits the Mech all that well - it's less inspiring and more ordering, in my mind. Having said that, there's no reason you can't re-skin it as command codes and give it the same effect.
Tech-Priest is a Tech-Priest, be it short or tall, unless you want it to be a story plot point that he's in a different role due to his differences.