I have seen many people doing this conversion. Please post them up! and what kind of mask works best to pull this off? I simply love that look!
NAG/JC H78 ALL THE WAY, FOR THE CASTLE LOOK IMO, JUST OPEN YOUR MOUTH UP A LITTLE WHEN TAKING A PHOTO AND YOUR GOT THE CASTLE STRETCH DOWN 
HERE ME DOING THE CASTLE STRETCH WITH MY NAG/JC H78 MASK ALONG SIDE NICK AND THE REAL HERO.
SOME MORE
**HOPE I COULD HELP
-JIM **
The important initials to remember there are NAG. Anyone from JC to AHG to Colin to Mo to Warlock, etc. can add finishing/eyecuts/etc. including Nik himself. Everyone sees things differently - I see Castle in the Nightmare, H78, 75K, Psycho, NMM78, (NO for the last two, or at least the Psycho that I’m for sure on) etc. Like dude above me said, just open your mouth a bit in said masks (if they fit you correctly) & you’re golden. 
"THE DUE ABOVE " 
MY NAME IS JIM
You got the vintage look down pat!