X-heads enough for 408 stroker?

A buddy of mine has a 408 in a 69 Dart and it has X heads with no porting, just a good valve job. 280/.474 Mopar purple cam, Air-gap intake, and 3.23 gears. Runs mid 12's and is very mild mannered. Runs out of wind at 5k but with 3.23 gears you don't need a lot of rpm.