Re: Royal Guard Helmet Dimensions?
Okay, I misspoke -- sorta -- out of too many years since I was more actively researching all this for my own purposes. When I say "Prequel" I apparently really mean "Revenge of the Sith". *heh* Here are the three versions we've gotten -- real-world chronologically...
Good shots that show front and back of the original helmet from Return of the Jedi, the first a costume test photo, the second a scan of a film frame:
Then, in Attack of the Clones, we only saw them briefly in Palpatine's office, and only really from the front, but the helmets actually look the same. Not sure if they re-used the originals or not... This shot is from the Visual Dictionary, and you can compare the avontail to the one on the Senate Guard helmet, next to him:
Which is relevant, because for Revenge of the Sith, they made new helmets with that same Senate Guard-style abbreviated avontail. Here's a costume test photo showing front and back:
Which is what it looks like you're doing. I'll get those measurements in the morning. For C, do you want it at that angle? Or straight front-to-back parallel with the top edge of the visor? Either way, my dimensions will be approximate. I have the wonderfully-accurate, copied-directly-from-an-original, I'm-amazed-they-got-it-so-dead-on Rubies Supreme Edition ROTJ (and AOTC) helmet, and I've modded a pretty accurate fan-made ROTJ style to the ROTS style, from photo reference. But no one's done an authorized, recreated-from-an-original-prop version of the ROTS Guard helmet, so take my measurements with a grain of salt. Also, this costume test photo from ROTJ shows the helmet in perfect profile, so you can see the front-to-back "flare" isn't as pronounced as in your model as it is now -- even with the avontail trimmed up at sides and back:
Hope this all helps while I get some numbers for you to plug in...
--Jonah