I have evidently mistaken a steering link for a front driveshaft. that bt21X was a unique car that happened to have a vaguely similar paint job to the photo. Is it therefore Roy Lane's Techcraft built BT21/28 - Buick?
Yes, well solved. It is the Techcraft-Buick which Lane built from a new Brabham BT21B chassis, and quite possibly the engine came from his previous mount, a BT14, although I'm not sure about that. He sold the car to John Cussins, who painted it orange, and is driving the car in the puzzle photo.
Lane's next car was 4wd, I think using a BRM set-up.
When I was checking my source, I noticed that the car was sold at auction in 2010, and the buyer was not at all happy that he'd bought what he thought he'd bought. I reckon back in the 60s , Lane was building his cars using all manner of stuff from his armoury, and no doubt cars got cannibalised, and the 2010 item was not all original.