Hi again, glaser 31
If the combustion chamber is 3 1/2 in diamater or is that the spigot diamater where the lip on the top of the cylinder fits in?
Its more than likely a 500cc engine, a 350 would have a bore size of 71mm (2 and 3/4in. app) and a spigot size about of 80mm (3 and 3/16in. app)
The head is from a Blackburne engine and this design came in from 1928 onwards engine type UT
Can you confirm the sizes I asked for in this and the previous message, this will tie it down better
The same design was used for 350 and 500 engines so photos are only so good
Regards
John O R