Okay, so I was downplaying myself about totally blowing the foam dimensions. It turns out that even though my starting assumption was the wrong in-box orientation, rescaling for the correct orientation barely changed the dimensions of my foam block! So, here you go
@maceffects, out of one of the two pieces of foam I've been modeling, the "Macintosh top cap" one is good enough to use for cost estimations, attaching as an STL file here, 1 STL unit = 1 mm. The foam block bounding box should be approximately 19.3 x 15.3 x 8.5 inches.
For Macintosh Plus (black and white boxing), Macintosh SE, and Macintosh SE/30. Cardboard box outer dimensions: 19.5 x 15.5 x 20 (vertical) inches. Bursting test: 275 pounds per square inch. Regular slotted contaner, bleach white exterior, kraft brown interior, two-color printing (red and black). The color boxing would of course be laminate printing.
Let me know what you find out!
View attachment foam-test.stl