These cars were built as gons by Thrall in 1952 and, except for the covers and wood sides replaced by steel, looked pretty much as you see it in the photo.  IIRC, there is a builders photo in the '53 Cyc, perhaps in a Thrall ad.  The Monon also got a one off caboose from Thrall at the same time that is known by Monon modelers as the ugliest caboose on the roster.  The Indianapolis gas company had a gas production facility on the east side near the Big 4 main to Cincinnati that made gas by coking coal with the by-product of coke.  Some of these cars, as well as some 40' cars, were converted to haul coke mainly to the mills around Gary.  However, I have seen a video of a train on the NYC in Ohio with a coke car returning empty to Indy from the east.

Bill Darnaby