I don't quite grasp what you are planning, but depth, height and width dimensions between Billy and Besta cabinets are completely different.
Yes and no. I have realized that the Fiskviken/Tombo doors are 64 cm long. The Morliden door is 192 cm long. 64 x 3 = 192 So 3 Fiskviken/Tombo doors = 1 Morliden in length. My idea is to buy 1 Morliden and 1 Fiskviken/Tombo unassemble both and reassemble combination of 192 x 60 (of course add custom glas). Therefore Morliden needs to be the same build as Fiskviken/Tombo that only differs in size.