Hmmm... reducing the ears might be the easiest solution. If necessary, there's also about 2mm of space at the top that you can recover by dremelling out the head pass-through as well. Another option might just be to scale the head well and have it non-transformable? Just pop it off the ball when converting to jet.
If you want to get a feel for how the face scales, here's a front-on photo of the head:
https://dl.dropboxusercontent.com/u/...head_trans.png
Are you able to set it as a texture on the front of the block head and and post a front-on render?
Edit: I'd be wary of scaling the head too small as the MP-03 seeker head is proportionally quite small to begin with, particularly the width.