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In NH that would be about a $50 used transfer case. I would look for a different one, put a part time conversion kit into it, and keep your transmission. That would be the cheapest route and you wouldn't be tossing away the money that you spent already.
Before you go any further make sure your transfer case linkage is not your issue.
Sounds like allot of work to change the transmission, and on top of that to swap to a standard too just because the transfer case has issues. Either get a used 203, or find a used 205 with the correct input spline count, and adaptor to bolt to your transmission.