"It is in the early A tuning, but that is an easy fix with a ruler and some Tippex ;-)"
There is an even simplier solution! It suffices to read the music as if it was written in the F-clef (like the lower staff on a piano sheet music), don't count the three first sharps (so if the original sheet music is in E major for instance, act as if the three first sharps weren't there (so no F-C-G) -> the sharp of "A" in the F-clef is a F in the treble clef, so the piece has to be played like a regular G-major one) and that's it! You can now play the piece on your banjo tuned in C. (hope my explanation is understandable).
Edit : by the way, I only get an error message when I try to access the pdf of this method, it reads like this :
Forbidden
You don't have permission to access /files/TUTORBOOKS/Eclipse_Self_Instructor_in_A.pdf on this server.
Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.