......... and that's where I found it. It was built in 1948 by none other than Les Redmond. There's a longish thread on a well-known site about a "mystery" engine and some discussion about how it was built, where everyone agreed to disagree. It could well have used aero-engine cylinder heads, possibly from a radial design, and the gearbox is almost certainly from a BMC A30/Minor.
Redmond was only 19 years old when he built it, so we can forgive him some naivety.