I went through A-4's with a Marine who had an issue with the canopy that had nothing to do with height - he (no s#!t) had to angle his shoulders off of square in order to close the thing. Once it was down though, he just wedged himself back to a 12 O'clock alignment and flew the bejesus out of that scooter. He never had any problems with the neck measurement either ...
But as 'pede said - we got rid of the A-4 (what a blast it was to fly those little rockets), and nearly everything in the inventory today is designed to accomodate just about any body size this side of freakish in order to maximize our pool of "human capital" (I can't believe I used that ugly phrase in this forum - sorry!). So you're PROBABLY ok.

Hey, Sponge - how is our diminutive friend doing? I was involved in that decision to send her other than Prowlers.