I would agree, as the NHRA Classed these cars in the D/SP Sports Class.
But, 'Back-in-the-Day {1968}, I do remember one of these 289/306 HP Sunbeam Cobra MK II cars putting away a 'hot' 67' Chevelle SS396
at our local Bowling Alley Access Road 'Drag Strip'.
The Sunbeam looked like a 'red missle', without a back seat.