Craig, there are no builder’s photos of the TH&B 4500-4799 series box cars because they weren’t built new for the TH&B.  They were USRA standard design 40 ton wood sheathed cars originally built for the New York Central and transferred by the NYC to the TH&B in 1941 to address the TH&B’s shortage of serviceable box cars (NYC was the majority owner of the TH&B, with the Canadian Pacific being a minority owner). TH&B gave these cars general repairs and new paint and lettering in their own shops and kept them in service , though in declining numbers, through the 1950s.  I’m sending you off-list a scan of a photo of a car right after it was repainted for the TH&B in 1941.  You’ll note that TH&B replaced the grab irons with ladders and added the Canadian standard sill steps at the ends,  Stenciling to the left of the door reads “to be used only for newsprint paper flour sugar or high class merchandise,” so these cars are exactly what your friend needs for his four mill, and are easy to model if he can locate decal or dry transfer lettering.

Richard Hendrickson