Do I need to replace it? I'd really rather not. Is the shape of the liner on the airborne helmet different from the regular infantry version?
Just use it if you don't want to replace it (or until you replace it) since it's only airsoft. A minor detail like that can be okay, and looks a lot less conspicuous than trying to pull off the 'Nam look with woodland BDU's or MOLLE equipment for example. Also, in regards to the helmet cover, hold yourself back from drawing anything on it. Writing/drawing things on helmet covers wasn't as widely done as most people think.
As far as using repro uniforms, most people wear them so as not to "destroy" originals uniforms by using them in the field. This makes more sense with WW2 airsofters and reenactors, since finding original uniforms can be hard on its own, as well as the fact that you'd be rolling around in 60-70 year old wool. With Vietnam however (in this case the 3rd pat's,) since the uniform stayed virtually the same up until the 80's, there's really no problem in finding original and post war production stuff and not feeling bad about using and abusing them.
I don't have my uniform on hand at the moment, so I'm not sure on the ripstop poplin. I've never really payed attention the fabric at all.
On jungle boots, don't use those $20 Chinese made ones they sell at surplus stores and come in black and OD. They're okay for the first time, but they fall apart when you need them most. Not to mention the color and quality looks nothing
like real jungle boots.
Here's some photos I've picked up. Looking at original photo's is one of the best ways to see how guys wore their uniform and equipment. It's mostly SOG and MACV guys (with the occasional WW2 photo I was to lazy to organize), but theres some grunt pics in there.http://s237.photobucket.com/albums/ff62/retrohead01/ww2/Vietnam%20War/
I'll post more links when I find them. I can't remember very many ever since the vietnamairsoft forum went kaput.