[Mister Pontiac]

I believe there is a simple solution to your problem. The mounts you show to bolt to the lower part of the core support are incorrect.

Take your shroud, lay it on the ground (fan opening down), and you will see that the radiator will 'lay' inside of it. At each of the four corners, there is a slot where a rubber "C" channel type insulator goes. That rubber insulators surround the corners of radiator tank/core seam, and the whole assembly then sits inside the shroud.

When the assembly is then lowered into the core support, there are two bolt holes on the lower portion of the shroud that allow it to bolt to the bottom of the core support. Up top, 4 bolts across the top.

The radiator hoses also help hold the radiator in position, but it's primarily those four rubber insulators shaped like a large "C" that position the radiator inside the shroud.

This is likely what you need:

https://www.opgi.com/cooling-heating...241268-st.html

Hope that helps!