543 0R 505

You could make the argument for either one.
The 543 will have noticeably more TQ, so the car would have to be up for that.
The 505 should make peak hp a few hundred rpm higher, but using the exact same cam and top end on both, I don’t see the 505 making a higher HP number.

Last fall we had a high CR 580” bracket race build with EZ heads on the dyno.

While not the optimum head for a motor that size, the motor pulled willingly to 7k.