Porting exhaust mani and o2

Hey, so i wanna port my exhaust manifold and o2 housing, and i know i can ship this out to get it done, but is there any way i can just do it myself??

Yea I have come across post of people that done it. I think they use some kind of die grinder and polisher. I dont know how well it works. I also dont know how they measured it to see if they matched up. More than likely they dont own a tool that can measure mm.