Dan, I'm not sure what it is you are asking.
Is your mini an auto? Are you asking if you can put the 4spd t-case from your 40 into your mini?
If so, then you can't. At least not without a whole lot of money and then your rear output would be offset. So while you have it, that doesn't make it a good deal.
You should be able to pick up a junkyard t-case pretty cheap for your truck, they aren't t-cases that people want, so I would think that the JY's would be pretty reasonable on one.
Have you looked into rebuilding yours and what makes you think your t-case is going bad?
Jack