You'll need to take both the intake and exhaust manifold together and let them machine as one piece so everything is even. If you have them separated you should rebuild the heat riser area....at least new gaskets and check the insulator plate to see if it is cracked. READ the "intake and exhaust" thread in the FAQs section.
here's the link:
forum.ih8mud.com
Its is a bit of a hike for you but J and D machine shop in Waynesboro did mine in December. It was $175.00 He does it on a table belt sander.
Why do you think you need it machined? Did you separate them? If not, you may get by with a new gasket.