GLFrontier is based on the Atari version of Frontier. I wouldn't hazard a guess how you could convert them. Why do you want to convert them and into what format?
Also, why couldn't you get GLFFE to work? You might have to update your drivers.
With regards to FFE however, all savegames should work between JJFFE, GLFFE and FFE3D as they are all PC ports, unless of course you want to mod the savegames. In that case you need a utility called Buffet and guess were you could get a download? Yup, you guessed it, Space Sim Central
Also, why couldn't you get GLFFE to work? You might have to update your drivers.
With regards to FFE however, all savegames should work between JJFFE, GLFFE and FFE3D as they are all PC ports, unless of course you want to mod the savegames. In that case you need a utility called Buffet and guess were you could get a download? Yup, you guessed it, Space Sim Central