Re the CJ T-18/D20 combo, the wide ratio T-18 was only available in the CJ from 1977 through 1979. Earlier years used the close ratio transmission.
The T-18 is probably worth a few to several hundred bucks to a CJ owner who wants to upgrade. This year range is the only widely known source for a complete WR T-18 setup for a CJ. Certainly it's worth less than the retail price of a Novak or Advance adapter kit. The T-18, adapter and (unique?) bellhousing is worth somewhat more than a Ford T-18 or other Jeep T-18s, just because it's ready to go without adapting or parts-mixing. How much more depends on the buyer's time, saavy and scrounging skills.
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D