Spartan army 400 - 390

[Marcvs75]

Question. Would it be plausible for the Spartiates of this period to wear the linothorax, while emancipated helots and peroikoi wore a simple tunic? Or perhaps the peroikoi, being merchants, wore the linothorax while the Homoioi did not?

This is certainly plausible. It s said that during the Peloponesian war Greek forces mostly abandoned their body armour (only two major hoplite battles in 31 years !!!). After that manny hoplites began to wear linothorax and musclethorax again.
The Spartans would als wear the openfaced pilos-helmet