I think it's a CYA too. I copied the following from the 5090 instructions

"These powerful heads use the stock location for intake flange and bolt holes, rocker shafts, and valve cover rails, for compatibility with original equipment and aftermarket parts.
Exhaust flange has been extended out .125” in order to provide dry exhaust bolt/stud holes. Exhaust bolt holes feature helicoil thread inserts for added strength and durability. Spark plugs have been re-oriented to a 15-degree angle to improve combustion efficiency."

With stock location for rocker shafts, valve cover rails, and intake flange, I don't see how it's possible that a stock valve train wouldn't work with a hydraulic cam that was mild street, under .5" lift at valve. I also like the dry exhaust mounts. I'm not sure about the 15-degree spark plug angle, because I'm not sure what good it does. Still I have 906 heads now and would get a 13cc chamber reduction, plus better heat transfer, and less chance of detonation with Edelbrock. And, the Edelbrock heads are made in USA.