FWIW, there's more than one way to skin the radiator mounting cat to ensure long life without leaks.
Although not yet blessed with a GT40 in my garage, I have a number of other cars including a Contemporary 427 Cobra replica with a Docking-like lightweight aluminum radiator. It uses a novel approach to remove stresses from chassis flex from the radiator itself.
The radiator has two tabs affixed to the side tanks, down low, which bolt to the underside of the main longitudinal chassis tubes. If the chassis twists (which I suspect it does, at least a bit), those forces would then cause the radiator to rotate about the longitudinal axis.
To securely mount the top of the radiator while isolating it from the chassis, this is the approach used:
Note that the arms are designed to let the top of the radiator swing side-to-side, while securing it in the fore-aft plane.
This radiator has now been going strong for going on 20 years with nary a drop of leakage. :thumbsup:
About Docking radiators--they seem to be made with some mystical properties, as they seem to cool better than same-size radiators from other manufacturers, based on my limited exposure to them in friend's cars of various types in the UK. That said, it's easy to get over-confident in them.
One of my friends is a lightness nut, the kind of guy who drills holes in everything in the name of weight savings. I've been hard-pressed to keep him from trying to put lightening holes in his tires! :laugh:
He had a Docking radiator custom-made for his Pantera; I don't know if it's smaller than their standard Pantera offering, but it's absolutely tiny, less than half the thickness of the (perfectly good, heavy, brass) radiator that came out, and a fraction of the weight.
Running down the motorway on a damp, dreary English morning, it keeps the car nice and cool. However, stuck in traffic on a hot day in Le Mans or Modena, the temperature rockets up to right on 260 degrees F and hovers there dangerously. I'm astonished his engine hasn't melted down completely; the fact that he has an aluminum block and heads may have helped his cause there.
The point being, don't get carried away with the wonderfulness of Docking radiators such that you engineer a sub-optimal design in the name of weight or cost savings. I suspect the Docking boys know a hell of a lot, and would encourage people to follow their advice, and if anything, err on the side of caution when having a radiator custom-made....