I for one like the 1693 idea. There is one used everyday here in town that has the Mack V-8 still running strong. The construction company that I worked for back in the early 90s had a Superliner with the inline 6 cylinder Mack engine. The thing that you need to remember that this is your build, and unless you are modeling an exact replica of a particular subject, you have some freedom of choice. If I'm not mistaken, the Superliner came out in the last days of the 1693 around 1980. A glider could have been bought in 1980 (or so) and a used 1693 went back to work in its new rolling chassis (among other possibilities). Something you might consider is putting round headlight bulbs in the headlight frames to back date it some closer to the 1693 era, but again the choice is yours. Regardless, around here things get swapped around all the time. I pulled a 72 Ford pickup into the shop one day and raised the hood to find a 360 Dodge engine (???). The point is that there is no wrong choice. You are doing awesome work by the way!