Put them on the block after its been finish honed to size...then scribe the bore to the head/chambers. Mark each head L&R So they go back on the same.
That's how you do it. You want it exact or a hair smaller than the bore...but definitely not bigger than the bore. Fyi most head gaskets are bigger , like 4.180 , than the 4-4.080 bores we use. And no, a ledge would disrupt and cause deflection into the path of the other air most near...and basically slow or crash the good air.=flows less n exhibits some turbulence perhaps
