QUICK AND EASY
The easiest and quickest way of fairing boat frames when you are dealing with odd grain direction, epoxy dags, and end grain plywood is with a belt sander and a course grit belt.
This is the only thing I use my belt sander for as far as I can remember. If you don't have a belt sander, dont' despair, a plane will do the job just as neatly, but will need to be kept very sharp on all that ply end grain.
If you don't have a plane, you are running out of options, but you could slice carefully with a saw and tidy up with sandpaper.