So, just because it has the 'Hellenic' (Google Fred Hellens frame builder) style rear stays in an extreme design doesn't automatically make it a GT,
It has a cantilever cable stop so it could have been late 1980s or early 90s. Beyond that, I doubt you will find out anything further
It is a mildly interesting frame no matter what and you could have fun with any sort of build
But it is not in any way a GT
Looking closer, it looks to have shimano dropouts, round cantilever bosses and reasonable braze-ons. If cantilevers don't fit, it may have been designed to use a u-brake or even rollercams which takes it up a notch from a d8mok bso
Just bare in mind the cantilever straddle cable may end up at eight miles long...