[nikbj68]

A couple of possibilities spring to mind.
It`s possible that to 'scratch rebuild' may generate greater profit for the company charged with the task, and bear in mind that although Autokraft were at the time the official 'AC Cars', they were not the actual manufacturer of the original Cobra.
Pure supposition on my part.
Secondly, Steve Gray, now the current official AC Cars` manufacture/service department as AC Heritage, would not put a car on the road that wasn`t mechanically sound. Period.
If the integrity of the chassis was in doubt, I am 100% certain that he would not have built a Cobra around it, nor would he be happy to race that Cobra on a regular basis, as he has done since 2005 or thereabouts, I`m sure his first outing was the Oldtimer GP at the Nurburgring, where he was awarded 'Drive of the Day', going from 93rd to 53rd.
Regardless of legal issues, I have no doubt that the UK 6036 is mechanically perfect.