There were at least 6 known changes with the Closed Cab body going into 1929:
From the MARC/MAFCA RG's and JS...
1.From Beginning of production through June 1928 the 1/2" flat cowl lacing was riveted directly to the cowl side panels; In July 1928 the cowl panel was extended out beyond the firewall;
2. There was a hole on the inside, lower left section for the Emergency Brake lever through June 1928...this hole was shortly discontinued when the Emergency Brake Lever was moved from this position to the Transmission Tower about June 1928;
3. Gas Tank...there were many changes with the 1928-1929 gas tank...Review this data to determine what you have:
http://www.plucks329s.org/pdf/gastan...29gas_tank.pdf
4. Two holes were added to the body sub frame bottom rear corner, Right and Left, in May/June 1928 so the Closed Cab could be adapted to fit the "A" Frame in conjunction with the "AA" Frame;
5. Four different designs of the AA-83725 Rear-Upper (Back) Panel were used as stated above and as stated on page E-80 of the MARC/MAFCA RG's and JS;
6. Also the placement of the outside Rear View Mirror Bracket as stated above.
There may be more that I am unaware of but do your research and you can come up with a "window of production".
Pluck