This cab I have is a brockway built cab, Mack aquired Brockway two years before my truck was built but the cab is older design. Brockway still built thier own bodies until 1973-74 when Mack started putting thier own modified R model cabs on and headlights, etc. 
Brockway was a carriage company from the 1850's and built thier first truck in 1910. Mack bought them out in 1956. Kinda like an Oliver thing. I guess thats why I like em, they both dissapeared around the same time. They closed the plant in Cortland, NY in 1977 after the workers went on strike. That Mack superliner, if I remember right has the wide chrome radiator with the Mack at the top center, right? If so that is what the 78 Brockways where gonna look like. My friend was at the Brockway factory sale, there was one superliner with Brockway emblems on it in a wind tunnel. I would like to have that truck! 
Oh well, more than you probably wanted to know about Brockways but I went to college in Cortland last year, thier historical society has a bunch of cool factory pictures and owners with thier new trucks. I was hoping to have my truck restored to drive to school, but never got to it. I'm going back next spring though, so it could still happen I guess. I had a nice job down there as a truck mechanic and bulldozer operator. Kenworth trucks and John Deere equipt. though. Good experience for me, since all I worked on prior was old tractors and bulldozers. They picked on me for liking the old Cockways as they called them,my dad always called them Rottaways. Everybody has a name for everything! Sorry to talk your ear off, Thanks, Adam