"Permission needed for use of GFX and music mainly but should cause no problems really." - Legally yes, but in the majority of cases no. For example, search the net or trwal magzine demo cds and you'll see many identical shareware versions of PacMan and Space Invaders for sale by bedroom programmers. Identical reamkes of games which haven't been for asle for years are not really a problem. The real rouble comes where you take a more recent game, or a character that is still being used and make NEW games...
For example a platform game where Sonic collects spliffs and robs banks would cause Sega to have a fit. However, near identical remakes of Sonic are all over the place and they don't mind. They have even granted permission for every one of their 8bit games to be released on the net for Emulation. Every single MasterSystem game for FREE http://www.smspower.org
has been around for years and never shut down.
Companies such as Atari and Commodore who don't exist anymore (Atari does in name but not the actual same company) are especially un-bothered by such things. For example, every single Commodore64 game is available for free at http://c64.com
and no1 bats an eyelid.
A few remakes are hardly gonna be a threat to anybody