Starting this topic since a similar one was posted asking about 70 Boss 302 built at NJ. Focus is on the Heavy Duty upper radiator brackets and some examples that appear to have received two additional screws installed into the bracket. These screws used holes punch in all of these brackets and screw into the upper inner lip of the radiator support. Best sources of course are unrestored cars since so many restored cars have had their radiator supports replaced. The presence of holes in the radiator support is what your looking for and you can always check for the panel date to get an idea if the radiator support is the original
These additional screws can be found on 69's also built at some plants but this focus in 70 Dearborn only. If we need to we likely will expand the survey to all Mustangs built at each specific plant and individual years. For me it was allot easier to find examples built in 69 at Dearborn
Notice that I found two different style screws. Arrows point out these difference and even though in the shadows an attempt to show how and where they perched and attached to the radiator support.
Will add the Dearborn posts from the other thread and we can carry on the discussions