You could use the Texel calculator to get a Texel number, pick a comparable U.S. listed boat from the Texel list and use the U.S. dPn of that boat.

If you are going to race, you should try to get a fair dPn for the boat.
While you may not care how you finish, it would be unfair to show up with a one-off boat with an incorrectly high dPn and beat other sailors who do care how they finish.
I have seen alot of bad feelings when that happens.