I put edelbrock victor jr. heads on my 377 which is the version with the 400 block and 350 crank. Edelbrock recommends not putting the upper steam holes in the beads, so I went on their recommendation. I am down here in south Louisiana and it gets pretty hot here. Have run the car on the street without any overheating problems at all. I am running 11.4:compression on pump gas, it runs 180 all the time, even in stop and go traffic.
It's my guess with iron holes you might need the steam holes, with aluminum you might not need them. Go with your after market head manufacturer.