Heidelberg
The only approved 427 was in the Robnell cars as far as I know.
I saw recently that Robnell has been purchased and there may be a rising from the fire. Although this may be a little off as the new owners focus is still on the electronics - Motec - and possibly the Daytona Coupe. Perhaps ring him..
I doubt if anyone including Robnell will get a 427 approved. The accepted standard is the current emission approved Ford quad cam and the GMH Gen. motors.
I do not think anyone has tried with the bigger GM motors..
Perhaps Cameron or Garrett may chime in here with their thoughts on the handling and performance with the Gen. motors and the Ford motors and the need for bigger cubes. Both have SPF Cobras from Cobra Tech.
Cobra Tech. are big supporters of the Cobra community and sponsors of a number of events. I would start and continue working with them - my thoughts. So perhaps keep talking with them..
An article in 'Kit Car' magazine weighed up the big block. v. smaller motor and Bob Bondurant was quoted as saying that he preferred the smaller motor for handling and driving capabilities.
There was also a reference to 1.2HP per cubic inche as an ideal combination for a Cobra. So a 351 motor at around 420HP was plenty. There was a lot of discussion on the over powering of the Cobra.
Look at the Factory Five race cars with the 302 cubic inche limit and the performance that these guys get out of their cars. I attended a race at Midstates and was amazed just how they handled and performed overall. I drove an Illinois FIA car at Evansville that was fitted with a 289 - it was both fast and handled well.
Mmmm everyone has differing opinions.
Keep looking...