Don't worry about what it might make for hp.
Just use the appropriate parts for the application and it will make what it makes.

As mentioned, keep the cam duration pretty short.

The 250 heads are a one year only, sort of odd ball deal.
They are essentially open chamber 516 heads with 1.74 exhaust valves.
So, they have the underwhelming 516 intake port.
Not really an issue for this type of build.
A little bowl work and a decent valve job would be worth it IMO, along with machining for posi-seals and setting them up with an appropriate spring.
Look the exhaust seats over good, if they're pounded out pretty wide, for that application, I think hardened exhaust seats would be a wise move.

Probably outside of your budget, but IMO the best way to update that short block would be to change the pistons to some KB quench domes.
It's really the best way to gain the compression and not grossly adversely affect the octane requirement........ Other than flat tops and closed chamber heads.