Proper license note for Maxima and Maxima-derived works

Dear all,

since I have modified the file merror.lisp and I need to redistribute a
small part of it it along with my program, which is released under the
terms of the GNU GPL v3 or later, I would like to know which is the correct
way to redistribute it. It is a very little modification, but doing things
in the right way is necessary.

First: what kind of copyright notice should I put in the header? The files
in my distribution have a header with such informations, but here I don't
know what to do. The original merror.lisp, as many (pretty all) other
Maxima source files, doesn't contain a rigorous license notice; it simply
states "The data in this file contains enhancements", with a simple
Copyright(c) with years and names, and no indications about the program
they are part of. There is a copyright notice in the main level of source
tree, with attached a GPL v2, but this doesn't seem the correct way to do
that. It is not clear if the license is the Gnu GPL version 2, or version 2
with the option for later versions.

Along with this question, I'd like to give a suggestion, but I don't know
if it will be simple since there is this text appended to the license:

"Distribution of such derivative works is subject to the U.S. Export
Administration Regulations (Title 15 CFR 768-799), which implements the
Export Administration Act of 1979, as amended, and/or the International
Traffic in Arms Regulations, of 12-6-84, (Title 22 CFR 121-130), which
implements the Arms Export Control Act (22 U.S.C. 2728) and may require
license for export."

Since Maxima follows the GPL, the file "COPYING" in the main source tree
should clearly specify which version of the GPL applies to Maxima and
derived works, explicitly stating "Maxima is released under the terms of
the GNU GPL version 2", or, eventually, specify also "version 2, or, at
your option, any later version".
Then, possibly update the header of source files with the proper note of
the GPL version. At the end of the license there is a clear paragraph which
specifies the right way to apply it, so it would be great (I'd say, it is
necessary...) if each file contained something like "This file is part of
Maxima. Maxima is released under the terms of the Gnu GPL, version...".

Sorry for bugging you with such questions, but I think it is important to
apply a license in the correct way...

Stefano