That is nothing but vicious rumor. The Boss block can support up to about 363ci, and that not only includes the 4.125" bore, but also the 3.40 stroke crank (common 347 stroke).
Not that I'm trying to cause a stink, but I keep hearing this misconception more and more.
The reason you are hearing the "misconception" is because there is a lot of truth to the statement
im not trying to cause a stink either... you can stuff a 3.4 crank in a boss block but the actual cylinder bore is shorter. So when you see ford saying "no clearancing for stroker cranks... less machine work ect." It is because the made the bores shorter and because of this shorter bore it pulls the piston skirts out of the bore. so yes you can do it but the block was not[/] designed for a 3.4 crank, if it was you would see 363 boss motors instead of the big bore 331's. I've seen this in person and my engine builder has been doing this for around 20 years so i think by now he knows his ****
you cant believe everything a magazine says, they have to support the aftermarket. How would it look if they denounced a brand new ford block?