Hi Don.
You are correct for a 1990.
However, those numbers stamped on the bottom of the fork tubes indicates that it was very possibly a different year.
If he can verify the numbers and measurements I posted I'm fairly certain I can tell him what they are for sure.
The 1990 KX500, kx250, and kx125 forks all used a 41MM chrome tube diameter.
That will be the nail in the coffin
My guess by the fork code is they are 91-93 and will be 43mm but, I have been wrong too many times to count