Tom, probably the true reason behind the chassis engineering is on account of the same company doing a 1971-3 Chevrolet Van at the same time they were doing the 69-74 Ford . Width wise , there were relatively close . I think it's interesting that they chose to do the "Slide side option as it really didn't catch on until the "Super- Snoot", uh 76-91 versions appeared . Oh sure , sliding doors were available from Ford . Chevrolets lousy dual action latches made a lot of , ( MY CUSTOMERS ) livid at the fact that the side door mechanism would break . This was especially true in the very early years of the "Door Extenders ", a product that was mandatory on Chevrolet vans with any kind of a wide tire . If you wanted the Fiberglass flares which I manufactured , yes, you had to run them .
Now Tom, are you going to do this van with a 240 six or the 302 V-8? I ask over the fact that there were TWO different Motor boxes that were used . The V-8 box was pointed at the rear and a good four inches shorter over all and came up a little shorter than the six . The six box was set out to allow the driver a greater access than the passenger side , was flat at the rear and was overall somewhat more vertical because of the length of the block and the height . Don't forget too, that the dash was designed two ways as well. The vans WITH a radio had a open slot beneath the radio . Vans without a radio could have had a lockable glove box . In addition, the 69-74 Ford Econolines also were the last to offer a "Flip- Fold " passenger seat too. These were a not too comfortable "Jump seat " with the ability to allow one to fold the back forward and then lift up slightly and fold it so as to allow a long load on the passenger side . Persons wishing air conditioning were treated to a somewhat abysmal set up where the driver got the A/C alright , on their side . There was also a very RARE auxiliary heater option too. It was located under the truck and on the drivers side . Also , in 1969-70, one could have ordered for the last time a Genuine Chrome FULL horn ring too !
I used to use my little known options at truck In's years ago when we would sit around a campfire getting sauced . Dodge also had some interesting quirks of options too.