The NAA steering box is almost identical to the late 8n steering box. Biggest difference is topcover/steering tube.
Sector seals and bearings are identical.
If it unscrews completely, and will come completely out of the box.. you'r in for money, and it may just be better to buy a complete box.. 've sene them in the 250$ range. If it only unscrews anout a half inch or so and then actually starts to steer.. then you are probably in business.
Main problem is the top bearing in the box dies from lack of lube. Steering shaft is a worm, and has a recirculationg ballnut that rides it... that ballnut engages the left (front)sector and drives it.. the front sector then drives the rear sector. The worm shaft sets on a bearing, and the race is mounted in inthe bottom of the box under a welsch plug. This bearing usually stays oil emersed unless the case is bone dry. The top bearing sets on top of the worm and it's race is held in place with the small cast top cover and steering tube. This bearing usually disintegrates. Same top and bottom bearings and races. you pull the top cover, pull the race if it is bad, and drop in a new bearing. Easy to weld the old race out with a mig welder.. a half inch bead makes it fall right out.
There is also a bushing/bearing int he top of the steering shaft that holds the wormshaft straight.
Top bushing is about 28 bucks.. bearing/race sets are about 20$ top, and 20$ bottom. Can't remember sector side seals.. but many rebuils and install a 0# grease like JD cornhead grease instead of 140# oil.
Seperate hood side torpedos from center rear hood, remove steering wheel, disconnect gauges and linkages.. pull hood rear dash, unbolt top cover.
Sector side covers are evidant.. 2 bolts each. There is a backlash adjustment stud on each side.. this adjusts the gear meshga and will tighten the steering up. Jack the front end up to do this.
I've got a NAA inthe barn I'm getting ready to tear down for this same job, I'm just dropping in the bearings and bushing.
Just did my 8n late last year.
Not a hard job.. just a greasy job.
If that's allyour needs.. you don't even need to crack the sector side covers.. just the top cover.. add new bearing, check top bushing reinstall cover and check steering. tighten sectors as needed, with adjustment stud.
If you do pull side covers, follow directions about getting everything meshaed back correctly.. there is a
master tooth ont he double sector.. makes it easier.. then you count teeth on the other and mesh at a certain point, etc.. same with ballnut.. count teeth and mesh with double sector front side..
The I&T F0-19 manual has a decent pictoral.
Soundguy