Auto tranny options

Still working on my Disco/SeriesIIA/4bd2t hybrid; I've acquired all the big pieces but I fear I can't use the Jatco automatic that came with the Isuzu motor because it's too long, especially if I go with a divorced t-case. The big challenge is to get the rpm's of the diesel down into the 1900-2000 rpm range at 70 mph. The 1.22 hi-range ratio of the transfer case pretty much cancels out an overdrive so I'll probably try to source a 1:1 high range gear set for the t-case. I would like, if at all possible, to use an automatic transmission and the relatively narrow rpm range of diesels (compared to gas engines) argues in favor of at least 5 speeds and a 6 speed is even better especially if 4th and 5th are od's.

What are my options for 5 or 6 speed auto trannies that are, more or less in order of importance:

1. short
2. have one or preferably two od ratios
3. short
4. readily available
5. short
6. adaptable to the Isuzu motor and LT230 transfer case