The predecessor to the Mack MC/MR chassis was the MB. I don't believe that Mack actually ever built a complete MB fire apparatus, but the chassis was widely used by Howe, Hamerly and a few other builders.
Engine 3, Reidville, SC
Mack MB/Hamerly
1000/500
Engine 3, Reidville, SC
Mack MB/Hamerly
1000/500