Let me try to be more descriptive. Each shock tower, both on the inside of the engine compartment and the fender well side has a beige ish color sealer on the joints where the shock tower meets the battery panel assembly and the windshield washer reservoir area panel.
Have never seen any applied in those locations. Sometimes we find a sprayed seam sealer or close application of sound deadener like material on the wheel well side in those joining points.
Additionally the radiator support joining those previously described panels has a seam sealer joint applied where the left and right panel join it.
Have never seen a classic Mustang or Shelby (any plant or year) that I recall having a sealer along those joints
Where those previously described panels meet the frame rails also has seam sealer applied at the panel weld joints of each panel. The color and type of seam sealer reminds me of the stuff General Motors used on its 60's cars. Mind you, this seam sealer is on bare metal with red oxide primer covering it then the black compartment paint?? Finally this seam sealer is also present on the panels joining the fire wall on the fender well sides.
Like the first response above have found spray on sealer on some examples from that period and plant along the front frame to inner panels. A dark almost black product
Maybe all explained since the car has been played with /"restored" in the past
No sealer in these examples
No sealer along the wheel side
No sealer along the radiator support to inner fender panel joint
Sprayed sealer along the rear lower seam
But the spray missed the upper seam on this example