Bit of a puzzle really. Its a nicely cast manifold, very substantial and nicely finished off outside and inside but absolutely no markings.
My thoughts now are possibly that it was fitted to a 50's/60's sidedraught engined car but it somehow doesn't feel old enough for that or, as John suggests, its a special manifold for a Shorrocks or similar blower from the 60's and early 70's when blowers were popular.
I will keep ferreting around.
Any help or advice gratefully received.
Chris