Brabham chassis ?
Yes! I will repeat that the only information I have been able to find about this car is talk on a forum, and the talk suggested that this car was built from parts of a Brabham. I have no proof. The engine of the puzzle car is probably not the one fitted in the Brabham.
(PS I realise that Brabham and Tauranac were Australian, but as far as I'm concerned a Brabham racing car was British because they were built in the UK)