This model was manufactured by Hartoy, Inc. in 1991 as part of their Hershey's Collection, which was part of their An American Highway Series, part #H51100. The model features rolling wheels, a removable trailer, and the trailer has resting wheels that can be flipped down. The trailer is a scale 21'6" long, 7'6" wide, and stands 12' tall. The truck itself is 18' long, 8' wide, and stands 8'3" tall. Combined length when coupled is 34'. Whether these measurements match the real Mack model BM I don't know. There is a spare tire on the back of the cab, and another one under the trailer. I bought mine on eBay, and it seems like they are quite easy to find, if you want one. I don't know if the "Hershey's" label is a valid prototype one, but since I model Pennsylvania, I just knew I had to have one. If you search Amazon and eBay, you will find this particular truck painted with different logos and in different colors, all made by Hartoy.
This is a close match to the model. Apparently the Mack model BM were produced from 1932 to 1941. They were designed to carry 3 to 5 tons.