I messed around with the hinge set-up today and got it worked out, including the cables.
The bolts you can see poking in will all have to be replaced with custom pins that will all be aligned and levelled, as well as some strategic bends in the hinge arms themselves, but it lifts and lowers with the faceplate in a good position out of my line of sight while open and a snug seal on the cheek and jaw when closed.
I've also welded a small tab on one of the hinges for the cable to pull the faceplate open. I haven't decided if I am going to have that cable relax against a spring to return, or just have a return cable to pull the faceplate down again.
I will experiment.
1. Side view. The screws will be replaced with flush pins and will not be seen in the finished helmet.
http://i.imgur.com/OMwphMt.jpg
2. Even though the bolts have not been trimmed, I was surprised that when wearing it, they still did not contact my face when closed. I'm still going to replace and shorten them though.
http://i.imgur.com/eR6dzws.jpg
3. Here you can see the rear boomerang hinge on the right side of the picture has a little extra tab welded on the end for the cable to attach.
http://i.imgur.com/tofmLBM.jpg
4&5. Rough placement/position of the cable and hinge positions when open and closed.
http://i.imgur.com/765JgiP.jpg
http://i.imgur.com/UjF0jvs.jpg
Now you can see why I have been reluctant to grind back everything to a nice finish. There's still a bit of fiddling, cutting, grinding and custom mods to go before I waste any time doing that.