Well lots , I would build more conservative with 430 or 470 CI max , but I have built a number of these & I have used stock heads as well , I would expect to see 375 ft lbs at the tires [500 range at the crank]on a Mustang dyno which sounds low , trust me it is not mustang dynos are very difficult to get a high # on .
From the point of view of flow the Stealths should win but using some tricks I have made Stock heads flow very well too , the advantage would be the closed chamber on the stealth heads & being alum you can run the compression in the 10.8:1 range .
At 500 CI you will need a lot of flow power band will peak around 5400 rpm which is great for a long life street engine with killer TQ
This is an example of fast racing [Factory Appearing Stock Tire] they have to appear stock , manifolds etc & run through exhaust with factory tires & running mid 10s to boot
https://www.youtube.com/watch?v=O3qSTsoo_v8 Crazy tricks throughout the car though to get that performance out of them !