DL109 Rebuilding

When did the rebuilding of the DL109 fleet take place? What I'm referring to is the removal of the side windows along the body and the streamlining of the roofs. It appears from every photo I've seen with the units up to the late 40's they had the as built windows along the sides, but pictures from the early 50's show the lack of windows as well as a cleaned up roofline, (also, the large engine number on the bottom of the nose.)

Did all the units get the rebuilding, or did some make it to retirement with original configuration of the roofs and side windows?

Wow, this one's been out there a while...

0740 was the first rebuilt by March 1949. I believe the rebuilding actually started in 1948, and there were several others completed in that year. 0740 was the only one that retained the original side sheathing arrangement with windows. The plywood sides were replaced by steel. There is a possibility it was rebuilt in the Hunter Green and Warm Orange paint scheme.

0738 and 0757 were rebuilt with the Green & Orange scheme as confirmed by photographs.

The first locomotive I've seen a confirmed picture for rebuilding is 0752 by May 1940.

All of the other DL-109s were rebuilt between '49 and '51. The windows were elimintated on all of them except 0740. The majority were repainted in the second variation of the Pullman Green and Dulux Gold that closely resembled the delivery scheme. It's possible that a handful of others were initially rebuilt with the Green and Orange scheme before. These seem to have been repainted in the Green and Yellow within a couple of years.