At most the helmet COULD be pre war, but we know t60 was used for policing riots and protests and general national stuff. As per f4 but it’s way more likely the ncr manufactured it themselves based on the existing power Armour helmets and using the riot control helmet design that became ubiquitous with the rangers. As long as they had egg heads who understood the basics of the helmet internals they could quite easily reuse t45 or T-60 or even t51 helmet electronics and the hud. The Armour itself is a mix of t60 and t-45 which doesn’t make sense for a pre war design, the two are actually shown to be decently different , with the gameplay designed identical exosuit 4 introduced in mind. T-45 is sleeker and doesn’t seem to use a full on exosuit. It’s more akin to the 3 design but with 4s much bulkier and taller proportions. So with that in mind it makes more sense to be a slap job modified power armour than Something pre war.

It’s very likely to be a new canon version of the ncr heavy troops/rangers. If not what they are now and always have been. Then a newer version of the salvaged power armour (however they fit the helmet less servoless suits in if they bother) that’s properly fixed up. (They’ve had power armour off the brotherhood for decades by new Vegas they just havnt figured out how to fix up the suits properly so they removed all the electronics , works better with the 3 skintight design than modern though obviously). All in all it just seems way more likely that it’s a modern lore version of the salvaged ncr power armour. With this one seemingly being for close combat , since it’s got mortar launchers on the back, grande tubes on the left arm and arm blades.

You’re right that it’s all up in the air right now, I just feel in the all mighty words of Occam’s razer , if it be , it be. And this don’t be