Problem with 1/2 in EM is that the anvil may be a bit too hard even for standard carbide. It all sort of depends on an anvil - what is it. How about you do a little test - see whatever you can file some of the top with a file. People also play around with steel balls and see the bounce. If you can file it even a bit - you can use 1/2 EM and lots of passes. Then you can do a little grinder pass with fine grade of sand paper.
Note that you should not remove too much - the hardened layer is not "forever".
If ball bounces a lot and you cannot file it is probably 50 HRC plus. Can be as high as 60 work hardened - remember it could have started as 55 but could gotten to 60 after a lot of hammer blows. For up to 60 HRC you need a bit stronger carbide.
People do cut hard stuff all the time - it is just hard on the cutter and machine. Hence why grinding is preferred.
When I dealt with old anvil I surface hardened I did not mill it - I used my hand grinder to make it flat. Hand grinder seems to be the way to go. Note there is a youtube video of someone "milling" a true anvil & how much pain it was.
https://www.youtube.com/results?search_query=milling+anvil
It all depends how hard things are - someone did one on a shaper with standard HSS - so it all depends on what exactly you have.