I had the same thing happen years ago on a set of original 1962/63 max wedge heads on my old bracket car, them dang Perma Toque gaskets melted a deep groove between the #4 and #6 cylinders on the block and heads
I had them both cast iron welded and had to have a shop, Valley Head service, grind both of them flat on their wet surfacing machine
All the other shops I contacted in SO CA back then said they wouldn't attempt to cut the block or the heads on their surfacing machines
You got really lucky on that block