I'm sure I've seen this somewhere else recently and as the man is Ing. Carlo Chiti, I think it is the ATS 100 V8 engine.
Yes it is. Simple as that. I thought it would be easily solved by a Rookie - the ID being the chassis tubes which prevented the engine from being taken out without the need to hacksaw first! Incredible to think that these top-level engineers hadn't thought of that.
I think Phil Hill's heart must have sunk to the floor when he first laid eyes on this contraption.
(PS to be fair, the extra chassis tubing was added later because the chassis flexed so much. Double bad, as they say)