Junkball and all curious,
To answer your question, there are anthro restrictions for helo's. They have the same type of measurement restrictions (butt-to-knee, sitting height, functional reach...) as any other aircraft. Unfortunately, the TH-57 compounds anthro issues because it has a seat that does not move up or down, so if you have a very tall torso like myself you can be restricted from helo's.
If it helps, I'm 6'4" as well and was anthro limited out of the tailhook and helo pipelines because of my sitting height. It's all about how you are proportioned and how your body will fit within the aircraft. Just remember, the anthro limits are there for safety reasons. If you aren't within the limits and something were to go wrong you might not walk away from the mishap (ie...going to eject and your head goes through the canopy before the canopy breakers).
My advice if you find you are anthro limited: first, ask to be remeasured. Sometimes getting re-measured you might find your measurements change. Second, if your measurements don't change sometimes waivers are unavailable (ie for sitting height) so you just gotta run with the cards you were dealt. Just remember, you will be a naval aviator and you will be flying!