I run big cams, heavy duty springs, and roller rockers and never had a problem with my 4.5/4.9 engines aluminum rocker rails. They rev to 6000 rpm all day long and never had failure on the rocker arm rail. I have also dissembled about a dozen 4.5/4.9 engines and never seen one damage. So I don't know. Are the Allante steel rocker arm rails the preferred ones? Yes. Can you still build a high performance engine without them? Absolutely. There are ways to make the aluminum rocker rails more resilient than stock.
Cheers

[This message has been edited by Johns 4.9 (edited 05-17-2019).]

quote Originally posted by Johns 4.9: ...You definitely want to use a longer rocker arm mounting bolt. Stock ones are only threaded about 2/3 the way through the rocker arm rail. I recommend tapping the rail all the way through and use a bolt that sticks past the end of the rocker rail by 2-5 mm.

So that's the trick!
I have never heard of one of these breaking. I have heard of bolts/studs pulling out, however.
Seems simple, in retrospect.

[This message has been edited by Raydar (edited 05-18-2019).]