There's already a lack of information online for simple things like torque specs. I can't imagine that a skilled professional could design the engine mounts even with if they had all of the relevant context online.

As far as I know, the way that these reproduction hardware companies operate is that they have physical cars that they can design around.

I have a 1993 Subaru WRX and I needed to replace the coolant header tank because mine had a bunch of leaks. I ended buying one from a specialty fab shop in the UK and I had to make a few measurements for them because there was varying bolt spacing for GC8 Impreza models.