If the valve guides have never been replaced they are probably well worn and beyond the point where new seals will reduce oil consumption.

At a minimum, you need to pull the head, check the surface of the head and block for warpage, correct as required, and install the head with a new gasket to get it running. Then you can sell it.

If you want to keep driving it, the head will need to be refreshed. This consists of new valve guides, maybe new valves, reseating of the valves, and surfacing the head if it has any warpage. Overheating can definitely warp an aluminum head.

While the head is off, the mechanic should measure the bores for wear to determine the health of the upper cylinder walls. It's common for these engines to need a head refresh by 100-150K miles, but the bottom ends will probably go to at least 250K and usually more with decent maintenance.

Most shops will remove the head and sublet the head work to a machine shop. As stated, make sure the machine shop has experience with these heads. The mechanic you chose to pull the head can refer you to his machine shop, and then you can check them out.

Duke