After I resined, fibeglassed and rondo'd the chest piece, I cut out the neck cover and made my own out of foam.
Here's it with the foam piece:
and here it is without the foam piece:
For the Grenadier knee's I plan to attachment to the shin piece, even though it's not 100% perfect to the game ( in Reach it's on your actual knee and moves freely) I won't be bending my knee other than to walk so I'll find it more convenient.
I'm wearing a size 12 steel toe boot and I didn't have to scale the boot at all for it to fit.
I hope this helps!