273 Overheating

A shroud it pretty much out of the picture at lower road speeds and can be a small restriction at higher road speeds. Unless shroud means something different than I normally think.....

Make sure you seal ALL gaps in the core support; I see some gaps at the top on either side of the rad in your pix..... I can think of one other thing you can try to explore another possibility after sealing the rad-to-core and rad-core-to-hood better. See if you can remove the hood bolts and put some longer bolts in with 1/2" to 3/4" spacers or stacks of washers between the hood and hinges. That will create an air gap at the back of the engine compartment to allow more overall airflow. This is not intended to be permanent but will be a partial test of better airflow through the whole engine compartment. (FYI, I have actually done this permanently on a turbo rally car to help underhood temps; it worked well in that case. It seems to allow both more rad air flow and air up around the engine too.)

If your temps do not drop with this and the rad/core sealing at road speeds, then you very likely just have too little coolant flow or rad surface.