TR6 Circle B heads

["SHANE Ingate" <hottr6@hotmail.com>]

Hi All,

Whats the story on Circle B heads?  I mean, I know that have a lot of 
material between the ports so that they can be opened up more than the other 
heads, but what years were they manufactured?  I have a Circle B head that 
come from pre-1971 cars as it has the big valves (1.45"/1.28" in/out).  What 
other difference are there between the early and late heads?  Will the early 
heads match up to later intake and exhaust manifolds?

Thanks in advance,

Shane Ingate in Maryland