Indian GP identifying Engine size

Hi
I seem to recall reading somewhere (but now cant find it !) a series of EXTERNAL cylinder head measurements that could be used to identify the engine capacity on Indian origin GP engines
saves having to take the head off
Has anyone come across these details please
Many thanks
I seem to recall reading somewhere (but now cant find it !) a series of EXTERNAL cylinder head measurements that could be used to identify the engine capacity on Indian origin GP engines
saves having to take the head off
Has anyone come across these details please
Many thanks