I have tested Catacomb 3-D in CatacombGL and I want to set it as the Classic Look, but the Aspect Ratio is 4:3 not 16:9 (320x200p). How can be accomplished?

Thank you for your interest in CatacombGL!
Unfortunately, the aspect ratio of the classic look is not adjustable and intentionally set to 4:3. The reason for this is that the CRT monitors of the early 90's had a 4:3 physical aspect ratio. That means the 320x200 image was stretched vertically to fit the screen. Some artwork like the compass in Catacomb 3-D looks a bit stretched as well due to this, but that's just how it was displayed on CRT monitors at the time of the game's release. The artwork for the compass in Catacomb Abyss was better fitted for the 4:3 aspect ratio, as it more closely resembles a circle.

If you want to know more on this topic, the doomwiki has an extensive article on aspect ratio.