1966 Ford GT40 Light Blue paint match

Try Gravity colors.  They make colors specific for race cars.  I believe this is one they carry.

Check out https://mcwfinishes.com/

Gulf – 2064 it blue, 2065 orange

The blue used on the Miles/Hulme Mk II in 1966 was not the same shade as the blue used on Gulf cars.  I believe it was Ford Night Mist Blue from the 1964 Mustang color list.

On a small enough model it probably wouldn't matter, but on a 1/12 car it should be noticeable.

You're right surface.  I recall a post over on MCM (your's Dan) where someone pointed that out and indicated it's Arcadian Blue.

MCW has this color

https://mcwfinishes.com/shop/ols/products/6633-arcadian-blue

I know this is 3 years late but here is a video of the "Ken Miles" car that the Shellby American Museum made about the car (the actual one used in 1966). Thought I would share even though I am years late.

https://www.youtube.com/watch?v=femuPHLQgu4