I've never done this, but unless you twin stick the case, then put air operated rams on it, it won't be button operated.... never looked at a jimny, but i think that there is always some way of making the speedo work, an adapter plate maybe? at a complete guess the speedo just count the revolutions coming out of the back of the case, sounds simple enough..... there is only a 4wd light on 1.3 case's, no engine management, and there is a pretty good gear calc on the good tech section....
hope it helps
vague i know 