The Master Cylinder is telling you straight.
The 'C' heads are okay for the street. It always comes down to what you're trying to do and how you're REALLY going to use the engine. For years, the sought after original equipment heads were the ECZ-Gs. Some of us have come to like the 5752-113s because they seem to have a little less valve shrouding and ALL of those produced were 'posted'. The 5750-471 heads are a consideration, too, if you're going to use domed pistons or a supercharger ($$$) or turbocharger ($$$) system.
Today, if you can see your way to do it, the aluminum cylinder heads that John Mummert and his son designed and are assembling after having them produced, are THE thing to think seriously about.
If you take a set of stock heads, have hardened valve seats installed, have them professionally ported, new valve guides, positive valve stem seals, new stainless steel valves, valve springs, quality one piece spring retainers, and quality hardened valve spring keepers installed, ...you might as well buy a set of the Mummert heads and be ahead of the game.
Out-of-the-shipping box and installed, the Mummert heads have been dynamometer shown to yield a ~50 horsepower gain over a set of the FoMoCo 113s!
Again, think hard about how you're going to use your engine build. Assembling a completely gone through y-block dead stock is not the most economical engine to rebuild. More than one of us has gotten caught-up in this endeavor. Thank the Lord, my wife hasn't left me yet! Remember, when you get all done, you want to be able to enjoy what you've done, too!
Hope this helps.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York