i have a rebuilt 6.9 liter from a 86 f 250. i am putting the rebuilt motor in a 1992 f 350, what class of automatic tranny is compatible. I took out the crappy 351 gas and putting in a real motor, the tranny is my real hold up. thanks for the reply

 

The I/N 6.9 liter diesel is at best rated at 170hp, and peak torque at about 335ft.lbs at a very low 1400 rpm's.

A C/6 automatic has more than enough strength to handle these numbers. Look for one from another diesel.

Other things to consider are transmission/transfer case output shaft spline numbers, drive shaft length, and rear axle ratio.

The door code on the '92 will tell you the rear-end ratio. If it's still there, and the rear-end is the same one upon assembly of the truck.