I have two 425's, one has A heads the other B. I have plans for them in the future but I don't know what exactly is different or how they compare to C heads.

 

A heads are 1965 heads, they have the weird rockers that may be obsolete, not sure if 66 rockers will adapt. The B heads are 66 heads but have the bump in the exhaust ports for the AIR bosses used on California emission engines. C heads are said to be a bit better flowing than the B heads but I doubt there is enough difference to notice on a street driven engine. B heads came on 425 Toronado engines in 1966. These would have the large intake valves and and the Toro a 39 degree cam angle where the 65 425 and 66 non Toro 425 a 45 degree angle.

 

Yes, the '66 and later rockers can be used on the '65 "A" heads by simply drilling the pedestals and using 3/8" bolts.

 

Hi,

Not sure if any advantage but A's don't have bumps for air injection not sure if B's do or not C's do.

Regards,
Jim