HRG Derrington Heads

[WSpohn4@aol.com]

I am trying to get a handle on the changes during the production run of  
these original alloy crossflow heads for the B series BMC motors.
 
If anyone has one of these, I'd appreciate you sending me the serial  number, 
and whether it is small or large combustion chamber, and small or large  (for 
1622 and 1798 engines) valves. The serial number is normally stamped on a  
horizontal surface at the back of the head.
 
Please note that I am only interested in original HRG heads, not the new  
replicas.
 
Bill