i think you may be refering to 416 castings, they are 58 cc chamber 305 high output heads, the came stock with 1.84 intake and 1.5 exhaust they were made up to 1982. they are decent heads, but they have limited flow, I posed the question "could i make the valves bigger?".the response was this, if you have a 1/2 inch hose and you need more water, adding a 3/4 inch hose will not give you more water because it still gotta squeeze thru the 1/2 hose .
461 heads are the old fuellies from the sixties to early seventies.thay are probably the best stock heads (with the exception of 461x heads , bigger ports)these are real rare, and still dont match up to a set of aftermarket heads .
the neat thing is, if you use the 416 ,s on a 350 you get instant 10.5 to 1 compression, lots of power, just no top end rev.good for a four wheeler, but not for speed.find an old set of 882 castings, they come 1.95/1.6 ports and can go bigger.882's are the best of the junk heads. mike