Yeah, i have had people tell me not to do 426 but no one with a good reason why not.. Everyone thinks 408 over 390 is a MASSIVE jump in power, but 408 to 426 doesn't matter... although it's pretty much the same price to do.
Because you will be horribly induction limited. All you’ll do is move the TQ and HP curves down.
Unless you have some very high end heads (and that’s not W2-5 heads…maybe a W7 or the big Indy head and even then the cross section is on the small side to make any power at other than John Deere RPM) you‘ll strangle the engine.
You could do sub 400 inches, shift at 7200 and drag a 426 by the balls anywhere you want to go.