That is a super easy box to rebuild, only a couple of moving parts, two bushings, and a couple of bearings. All the little parts are available through the venders listed above plus others. You can find the bushings local if you have a bearing dealer in town. One thing I did to mine that really helped was to add a second bushing in place of the spacer bushing ( Bushing 6.655 ) in this picture (
http://chevy.oldcarmanualproject.com/parts/1929_54/396.htm ). It added a lot of support out on the end of the sector / pitman shaft. The ( Bearings 6.530 ) are a barrel shaped roller bearing, unique to the steering boxes, you have to get them from one of the venders above if yours are bad. If they are bad, it will be the lower one from water infiltration setting on the bottom of the box. The races are part of the steering shaft, if they are bad, you are looking for a used replacement shaft, as new replacements are not available. Follow along in this manual when it comes time for adjusting the assembly, (
http://chevy.oldcarmanualproject.com/booklets/52mts20/5220mts01.htm ) Its for the new style gear box, but the adjustments are the same.
If you really want to upgrade the steering box, look for a '41 - '46 steering box. I believe there is one in the for sale section of this site right now. The newer box has roller bearing steering, not quite like power steering, but one heck of a lot better then the gear to gear box you have now. My '37 is up graded and drives like a dream. It's a bolt on upgrade as long as you have the steering wheel that matches the gear box. The '37 - '40 wheel is keyed, the '41-'46 is splined. Its well worth the trouble to upgrade.
