Im not completely sure but i think the existing sleves are removed, the holes for the sleves enlarged ( if necessary ) and a new sleeve installed by cooling it alot and pressing it in place. You could of course just set your block up on you mill and bore it out a little, maybe 20 thou. That is a little more common.
trust me mate get the pros to do it ive been machining for 4-5 years and have got to know a lot about doing
these things it aint worth trying to do it on your own you would fuck it up i know people who r the ultimate kings at machining and they have fucked it up it takes time and experience thats why the costs are high
the thing is that i have an uncle with 45 years experience on manufacturating with milling machine and laythes. What he needs is a schematic of the engine block with the tolerances and surface finshes for the block. (the layer after the sleeve)
You would need to bulid a fixture to hold the block, you would also be required to invest in the tooling for the actual machining operations, if your miller is not set up to spray coolant you destroy any surface you try to machine. So on and so forth. It's not only safer to have a shop do the work it's cheaper.