T-4 is basically a T-5 without the overdrive. For your use, while it's not the most durable trans, the T-5 is probably the best choice since it has overdrive. It's fine as a street trans if you aren't abusive and take proper care of it. TF999 would be your choice for an auto, that was the stock unit for your year. The TH400 was only used with q-trac (full-time 4WD) pre-'80 so it would require adapting to your Dana 300 t-case or you'd have to get one out of an older FSJ that's mated to a Dana 20 t-case (which then gets you into fitting it up to your later model frame). You're going to need to spend some time and money on the suspension & steering at those speeds.
'86 CJ-7 Laredo: 4.2,T-999,D300,D30/D44,'94 YJ tub, full cage, Shrockworks rockers, OYR corners, AC,cruise,restored seats,3 tops,2.5" Superlift,F-T shackle reversal, RS9000x's,35" Dunlop Mud Rovers.
'83 Scrambler: time & money pit under construction with parts from CJ's,YJ's,TJ's,FSJ's,GM,Ford,IH,Honda,Toyota and a whole lotta aftermarket & custom stuff.
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