i'm going to put a dana 18 transfer case on my
75 cj 5. i was thinking i could cut my old d20 case in half and just have the input-rear output shafts. this would go in between the tranny and d18. could this work?

How would you shift it if you cut the right half off? How would you bolt the input of the 18 to the output of the 20? Can you make adapters? There's not enough room in a CJ5 anyhow for the extra length.