"Split-Case" Transfer Cases came factory in 8/80' - 1/90' FJ40, FJ60 and FJ62 Land Cruisers. They derived the "split" name as they require being "split" to remove or install them on the vehicle unlike the earlier 1 piece cases. These cases came in at least 5 different configurations, most changes being minor with the exception of the idler shaft change. In April of 86', The idler shaft changed from its original 34mm OD, to a slightly larger 38mm OD. This makes external identification of the transfer cases rather easy. Simply use a set of calipers to measure the idler shaft where it protrudes from the rear of the case. With the change in idler shaft dimensions, bearings, seals and internal gears were also slightly changed.

34mm Idler - Manual Trans. Setup (H41/H42/H55F)
(8/80' - 4/86')
Input shaft: 19 spline
Input Gear: 34 tooth
Primary Idler: 45 tooth
Secondary Idler: 25 tooth
Hi-Speed Output Gear: 34 tooth
Low-Speed Output Gear: 43 tooth
PTO Gear: 31 tooth
Total Low Range Reduction: (45/34) * (43/25) = 1.3235 * 1.7200 = 2.2764

38mm Idler - Manual Trans. Setup (H41/H42/H55F) & Auto (A440F)
(4/86' - 1/90')
Input shaft: 19 spline
Input Gear: 32 tooth
Primary Idler: 43 tooth
Secondary Idler: 24 tooth
Hi-Speed Output Gear: 32 tooth 
Low-Speed Output Gear: 41 tooth
PTO Gear: 31 tooth
Total Low Range Reduction: (43/32) * (41/24) = 1.34375 * 1.7083 = 2.2956

38mm Idler - Manual Trans. Setup (originally mated to H55F - Non-US Application)
Input shaft: 19 spline
Input Gear: 32 tooth
Primary Idler: 43 tooth
Secondary Idler: 26
Hi-Speed Output Gear: 32
Low-Speed Output Gear: 38 tooth
PTO Gear: 31 tooth
Total Low Range Reduction: (43/32) * (38/26) = 1.34375 * 1.4615 = 1.9639

8/80' - 10/82' - 34mm idler shaft, unique input gear. No oiler cup provisions. No spacer bolt hole.

10/82' - ~83' - Same as earlier case, with updated input gear. Introduction of oiler cup provision at this time. Middle bolt hole not present.

~83' - 4/86' - 34mm idler shaft. Has oiler provisions. Has spacer bolt hole.

4/86' - 8/87' - 38mm idler shaft. Has oiler provisions. Has spacer bolt hole. Different gear train, bearings and seals from 34mm cases. 

8/87' - 1/90' - 38mm idler shaft. Auto tranny version. Vacuum 4wd. Has oiler provisions. Different gear train, bearings and seals than earlier 38mm cases. 

4/86' - 90' - 38mm idler, no oiler (might have been an auto one I had without oiler provisions?)

Determining the year of a Split-Case:

Split Transfer Cases were stamped with a serial number or "build code" at the time of manufacture from the factory. Using this code, you can derive what year transfer case you actually have.

The T-case serial number is a combination of date code and serial.

The format is YMxxx
Y = Last digit of year (always going to be
M = Letter corresponding numerically to month
xxxx = Serial number of case that month

If the number on your case is 5 I 5858, that would be 1985, I=9th letter = 9th month= Sept., 5,858th case built that month

See images below for two other examples.
First is 6J4694, located at edge of PTO port, 1986 Oct. #4694
Second is 9K149, located on top of case, 1989 Nov. #149.

(Special Thanks to Jim Chenowith of TLC Performance & the Ih8mud.com community for deciphering the code and providing the pictures)

Vacuum Shift - Manual Shift Conversion

It is possible to convert the 8/87' and later split transfer cases to manual operation, identical to that found in the early versions. Below is a list of parts needed to perform the conversion:

90254-05004 - Roll pin for front axle operation rod
36313-60050 - Rod front axle
(Then you need a hollow 15mm nut, spring, and ball, drill and tap which is common to 34/38mm manual cases)

36307-60030 - Lever arm hi/low
36362-60040 - Gold cad arm for lever above
(Also common to 34/38 manual cases)

The machining is there for front rod seal.

(Courtesy of rick_d @ ih8mud.com)