Wow, this is a stunning design I haven't seen before, I was going to quit posting for the night and get some sleep... but then POW this popped up on my screen. 1928 Brill Doodlebug converted to a rail defect detector car in 1954

Union Pacific Railroad DC-3 at Lincoln, Nebraska on an unknown day in October 1956, 

The DC-3 was built by the J. G. Brill Company in 1928 as Detroit & Mackinac 201 on Order 22749. As built, it was powered by a Hall-Scott 300 horsepower gasoline engine and GE electrical gear.

 It was purchased by Teledetector Company of Chicago in 1954 (along with D&M 202, same builder and construction date), and converted to a rail defect detector car. Apparently Teledetector was planning on competing with Sperry, but only the 201 was converted and was sold to the UP in April 1954, becoming DC-3 (03000). The DC-3 was modified in August 1961 (renumbered 90300 but still displaying DC-3) and again in 1984. It was sold for scrap in December 1986.

Description: Union Pacific Railroad DC-3 at Lincoln, Nebraska on an unknown day in March 1962, Kodachrome by Dick Rumbolz, Chuck Zeiler collection. This appears to be the second permutation of the DC-3 on the UP.

 It started out as a gas-electric built in 1928 by the J. G. Brill Company on Order 22749 as D&M 201. It was a Model 350 powered by a Hall-Scott 300 horsepower gasoline engine driving GE electrical gear.

 It seated 38 passengers and weighed 58 tons. 

In 1952 it was sold to Teledetector Company of Chicago and converted to a rail defect detector car. However, the company did not survive and sold the detector car to the UP in April 1954.

 It became DC-3 and still had the as-built Brill front. It was rebuilt in 1961, acquiring the brow over the front windows as seen here, and rebuilt again around 1983, acquiring yet another front end arrangement. 

Note that in this arrangement it has a single headlight and the Brill passenger windows were retained, to be replaced at a later date.

https://www.jalopyjournal.com/forum/threads/vintage-shots-from-days-gone-by.428585/page-6046#post-12920604

http://www.rrpicturearchives.net/locopicture.aspx?id=153136