They're not typically located in the Eye of Terror, so you wouldn't expect quite as much warpstress on Alpha Legionnaires. That said, the warp reflects reality and reality reflects the warp, so being chaos marines they are still little beacons of the warp, so some amount of warp stress wouldn't be unexpected.
Being based away from large warp disturbances also suggests to me that they won't have 'benefited' from the warp time dilation effects other legions have endured, meaning many Alpha Legion sects might have been running the full 10k years since the Horus Heresy.
This a lot of time in which they will need to keep their equipment up and running (or finding replacements/spares). It suggest that while they won't have Mk V Heresy armour proper, as they will have looted a lot of mark
VI and VII in the interim, they will maintain the jumbled appearance that comes with Mk V.
It is my opinion the current
CSM codex best represents warbands that are a mix of the splintered factions that once were legions. As such, I've built my current space marine army around a mixed legion force united under Abaddon.
As part of my force I'm working on a squad of Alpha Legionnaires, they use a mix of chaos and loyalist parts, minimising 'warped' components and I've largely avoided mutations (except for the champion, who gets two heads because hydra).
This is my progress so far with my vision of
40k Alpha Legionnaires:
Everything is still
WIP so if you have any CNC please
PM me (I don't want to hijack this thread)!