Getting a higher voltage from TL431 in a crowbar circuit
You want to 'set' the TL431 to your desired nominal crowbar voltage. Read the TL431 datasheet and look at the block diagram to understand why.

You also likely will want to reduce R3 considerably. The TL431 needs 1mA, so maybe a couple hundred ohms. Otherwise current will flow thorough the gate unnecessarily before it is supposed to trigger. Probably not enough to trigger it, even under corner conditions, but there's no real advantage.
Agree with Andy, set up a free simulator such as LTspice (you may have to add the models for the parts) and test this yourself, then ask questions if it does not make sense.