The T1 chinstrap on the rear seam M1icon shell is the same as on my 'Vietnam' M1 pot, so yes may well have been reconditioned for Vietnam.

The liner has a later OD#7 headband (dark olive drab), post WW2, that would have been used in Korea. And maybe Vietnam? Probably, but not sure.

Like all military gear, things got swapped around, regardless of how it was when first made. And who knows what happened after military service. The best you can do is to put them together as they might have been. Either M1 shell could have been used with the Firestone liner in WW2 (but with lighter OD#3 webbing and chinstrap) and may have been used together for Korea and Vietnam. The T1 chinstap is Korea or Vietnam. And obviously the camo cover is Vietnam.

If they were mine, I'd try to find WW2 nape and headbands in OD#3 and a leather chinstrap (nothing wrong with adding repros) for the Firestone liner and put it in the front seam M1. With that original paint/cork, it would be a great piece.

Then find another liner and make up a Korea (or Vietnam) pot with the rear seam M1.

Regards, Charlie