"Sleeving" integral machined cast iron valve guides such as those used on older engines with cast iron heads is a typical repair procedure, but aluminum heads always have separate valve guides, usually a bronze alloy, that are pressed into the valve guide bores with an interference fit.

Changing them is really quite easy for a properly equipped engine machine shop. The head is heated in an oven to about 400 degrees. Then the guides are tapped out and new guides are tapped in. The 400 degree temperature expands and softens the aluminum making it easy to remove the old and install the new guides.

IMO it's best to place the head back in the oven, turn off the heat, and let it slowly cool. This will minimize the chance of warpage.

New guides or sleeving old guides requires head removal and disassembly. Also, since the new guides may be slightly off center from the old, reseating the valves is mandatory, and if the valve stems are worn more that about half a thou or if the seat margins are thin they should be replaced. On an engine with fairly high mileage the inlet valves can often be reused, but exhaust valves are usually more worn and require replacement.

Duke