Bugger, you don't have to believe me but I never spotted it. My thinking went like this just to show you how little I know and how much of a guess it was.
The sheer bulk and the inlet manifold made me think Dorman. But it is not a Dorman but Dorman had something to do with McLaren. The Rocker Cover's very very similar to a smaller McLaren Ricardo at Charity, so knowing Mclaren had connections with Dorman, Ricardo and Petter I kept my options open with just McLaren. So we know make, anyone guessing model? My guess M series, so M3, 1940-1956 60-80-HP. Crane or Shunter.
In a Skip?
help save a mclaren MR4 Mk2.................
From the above thread. "MR4 is 2 valves per cyl, indirect injection and air start with a Petter W11 compressor; while the M4 has four valves per cyl, direct injection and electric start"