Certainly false if the wording is taken literally (and in my opinion it's their intention).
Missing from the text but assumed by Clifford "* when combined with other modifications*". These would include a very different cam and springs, extensive porting work, valve and valve seat mods, and (in a 235) stronger connecting rods. Not commonly performed but helpful: efforts to reduce cranking pumping loss and control oil behavior.
Even so: the head, or specifically the intake port, is a dead end, even compared to other siamese ports of the same era. It can be made better, but it's limited by the design as well as the casting itself - adding 90 hp? When Satan skates to work.
As to the product offered:
It appears to be a synchronous (non-progressive, look at the geared throttle shafts) Weber - 38/38?, unlike the Pinto 32/36mm Holley 5200 frequently used in a different way.
The large plenum volume will add some peak power. I'd give the supplied air cleaner a pass, but not 5 stars.
The header is obviously an improvement (over anything but the Corvette exhaust), although I would have recommended 1/8" larger primary tube for the #2-3 and 4-5 exhaust ports.
Still needs a distributor curve correction, either a mod to the original or an HEI etc. conversion.
I've never driven or installed these parts, but the engine will deliver more power, and a very annoying variable ("what jets do I need?") is claimed to be resolved.
Unless you have a Plan B...? It will be faster afterward, if that's the goal.
* you'll find this disclaimer at the bottom of many speed equipment claims going back 70 years.
