An advert was featured in CVG June 86, with it stating that the C64 version would be available soon. Of course, we never did get to see the game, and Tir Na Nog became the only Gargoyle game to be released on the C64.
As some extra trivia, there was a competition ran in issue 55 of CVG for winning a copy of the C64 version of Heavy On The Magick, but we doubt that the winner ever got a C64 copy and maybe got something else instead.
Jon Simcox confirmed in 2017 that he was the programmer on the C64 conversion, and the game was cancelled, as Gargoyle Games decided to focus on arcade games, hence the FTL label was created. The game was actually almost complete, but it seems that the conversion is now long gone.
Without much chance of the partial conversion now being found, it could well soon be a case closed!
Contributions: Peter Weighill, Nic, Jon Simcox