[Mike Taylor 3601]

Cutting the head is different from the block,the Isky tool everyone is talking about is for the block ONLY not the head. BHJ makes tool for heads has plate similar to torque plate that bolts to head to locate cutter assm.
You can cut head on boring bar or mill but you have to have a way to center it or locate so you can cut the grooves in the correct place,when you do the block you locate off cylinder bores like you do when you bore cylinders,the head does'nt have a way to locate where to cut.
Someone that is real good on bridgeport w/ dro could map the bore centers w/dowels as reference point then transfer that to head and locate bore centers and cut the grooves,but it would be big job to do that way.

I don't know what kind six you are workin on But if it has same bore centerline as a V-8 someone has plate for to cut receiver grooves then could possibly adapt to use on 6 cyl.
Mike Taylor 3601