I got to tell you this: I´ve measured most of these camel hump heads (#186, #291, #461, #461x...) intake ports myself last winter, and they really were all the same. ALL OF THOSE CASTINGS MEASURED 165cc, INCLUDING THAT #461x.
I located tens of pairs of these old camel hump heads just by accident from a wrecking yard, and I was wery eager to return there again and measure them to find a superior head for few dollars. You can imagine my disappointment when I finally got to measure the intake ports, and they all were the same! Really! The intake port from a #461x is just as small (approx. 165cc) as from a #291, for example.
I had read from Hot Rodding magazines that there are some superior big intake port camel hump and fuelie heads cast by GM, and I thought they were either #461x, #292 or both. So now I know the superior head definetely is not the #461x...
On the latest Chevy High Performance Magazine there are quite many SB Chevy heads measured (both the intake ports and combustion chambers), and they even flowed them on a flowbench. It´s a VERY good article! One camel hump head was there, namely the #492. Their measurement did not end up as big as mine, I think they got 159cc, but I´m not sure. Gotta check that article again. Anyway my measurements are from stock heads, not ported, so what could be the difference between the magazine´s and my measurements? My measurements may be off by 1-2cc, but no more.
That wrecking yard I visited has got various types of those camel hump heads lying around. Ported, stock, with valve seats installed and without, small and big valves, screw and pressed studs, complete and bare, some cracked, some not... They cost less than $300 a pair. That may sound like cheap, but I wouldn´t install any of those heads straight without first checking (and maybe machining and fixing) them.
And to answer Bryans question: the main difference (in my opinion) between a #462 and a #461 (x or not) is the combustion chamber size. The #462 has got the normal approx. 64cc chamber and the #461(x) has got a bit smaller one with approx. 60,5cc. Just as Scooter said. So with the same pistons you get more compression (=power or problems...
with the #461(x) heads.
Bryan, you said you´ve got #292 heads there. PLEASE VERIFY THE INTAKE PORTS OF THOSE AND THE #461(x). Put an intake valve in it´s place in both heads and check which head´s intake port will swallow more water. By doing that you could end this never-ending debate about mystery GM SB heads! Please do that and try to be accurate. No accurate cc number is necessary, just the fact whether they are the same size or not.
I mean you could do me a BIG favor. I´ve been searching those "mystery" big port heads for some five years every time I went to a swap meet or wrecking yard, and I´ve already given up because I thought the best ones were the #461x castings. But what if the #292 is the one? You would send me on a mission again by telling me that #292 intake port is clearly bigger. I don´t care how much bigger, just the fact would put me on the road again.....
Million thanks already.