You can use an early Xploder tranny(4.0L specific), but the first gear is not as Low as the 2.9L version, thus its stronger, but less aggresive.4x4junkie said:The Mazda M5OD-R1 is the strongest of the manual trannys that came in the midsize Fords. A similar version (M5OD-R2) is used in F-150s, also (this one won't bolt up though.)
The Toyo-Koygo and especially the Mitsubishi FM 145/146 transmissions had a lot of input shaft bearing issues.
A M5OD-R1 from a 4.0L will bolt up to your 2.9L.
Look in any 4.0 Ranger or Explorer (non SOHC) for this trans.
The 2.9 is a good motor, the only real weakness is if the cooling system fails (stuck thermostat, etc) it can crack heads easy. This rarely happens at normal op temps.
I swaped a 4.0L into my 86 BII and the 2.9L radiator does the job with no problems. I just used the upper hose for the 4.0L and the lower hose from the 2.9L. mine never goes over 190.If your worried about over heating, put in a 4.0L radiator (bolts in) and you wont have problems.