Ford had hp ratings for the 390 that ranged from 250 to 401. The base 390 4v was 300, the police interceptor was 330 (solid lifters), 390 hp 4v was 375, 6v was 401, the Tbird with 6v was 340. I know the 390 GT's would hold their own against the 396 Chevelles up to 360hp. I would guess a 390 gt would be around 350 at the flywheel. I saw one on a chasis dyno, the owner said the engine had never been apart at it had around 65,000 miles on it and it made 280 hp at the wheels.

a few ford engines were overated...but not the 390...335 is probably optimistic...