Modifying std header for cj port heads

I'm trying to open up the bolt holes on my headers so they match the port roof of my TFS heads. I'm trying a dremel tool with carbide bits and it sucks. Holding a drill bit to the side seems to work better. Any suggestions?

Make sure its a high Quality bit or a mounted stone and what ever tool you use is high rmp ie die grinder

Put it in a bridgeport and use an end-mill.  Otherwise, use a hand held die grinder with a 5/16" carbide bit.

Ok thanks working on getting a die grinder now. These headers aren't going back on until I make them work right lol. 9s or bust

Got the headers all matched up hoping for some positive results from it. It has to help.