Just an educated guess...
Without having further knowledge about this project, I would guess 1939 and 3 litre engine.
Yes it was advertised as a 3 litre and I think I'll give you the point as I believe this proposal dated originally from the very early 1940s.
It was oddly advertised in the motoring press in 1943 perhaps as a reminder of Aston Martin's glorious past.
The ad appeared to be a 15/98 chassis to be fitted with Claude Hill's proposed 3 litre engine, a 6 cylinder OHV that was never built. The ad contained a quote from Matthew Arnold stating 'The great aim of culture, the aim of setting ourselves to ascertain what perfection is, and to make it prevail.'