Even if you get the parts from Curtis, would they be adequate for a 420,000' flight? His products are fine for model rockets, but something like that surely needs an engineered solution.
There's a lot to learn from an attempt that is 20% lower.
No question.
But that's a different rocket given that the current stack is "all motors" and the "motors" are done except for casting propellant......new HW....new sims...new paperwork.....pretty much a reset.