I'm not sure what you mean by "worm gear". Are you talking about the hydraulic controller on the end of the steering column?
And I think you may have your model number a bit off. Tucker's model numbers, at least until the 2000 series had this form:
first (and later, second digit) = series number - i.e. 400, 700, 900, 1300, 1500, 1700
second (or third in two digit series)= number of tracks - i.e. 4-track (model 443, 743, 1742) or two-track model (222 - just two tracks, no skis ,323, 423 - two tracks in back and two skis out front)
third (or fourth in two digit series) = number of doors - i.e. 442 has two doors, 1644 has 4 doors, 743 has three doors.
Tucker made several models that were not much more than a bare chassis with seats. Those were the xx0 models - no doors.
For a look at this, go to:
http://www.safetyoneinc.com/specsheets/pdf/TCKR400A.PDF
If the spec plate on the dash says "model 440AC" I'd suggest the cab is not factory.
Still a beautiful, fine lookin' 'Cat.
Jeff
owner of a '77 1743 (the "runner") a '78 1744 (the rusty parts machine) and a '49 423 (the retirement project - if I can get to retirement) and former owner of two '78 1743s