This is an interesting question. Phase II was introduced in 1974 and phase III in 1976. P40 and later p42 locos did not come in until 1992.
The initial livery to me seems like a combination of Phase II and III schemes, likely unique just to P42s.
Phase II had wide red/blue stripes and very thin white stripes in the center and on the outside of the band.
Phase III had even bands of all 3 colors with no outer white stripes.
The Kato P42 has wide color stripes and very thin outer white stries, but the center white stripe is much wider than Phase II. Where the band wraps onto the nose and get thinner, the color bands get narrower which the white center band remaining the same width, with the very narrow white stripes remaining on the outside edges of the band. That looks more like Phase III, with a touch of Phase II remaining.
See
https://en.wikipedia.org/wiki/Amtrak_paint_schemes1993 Photo.
The only P42s painted in true Phase II and III schemes were the special heritage units:
Phase II
Phase III