Head work isn't really difficult. It does, however, require some special tools or the time of a machine shop.
If you have a correct 1948 head all ready to go, you can take it apart and clean it to see what you got. Label all the parts as to their position. Take the valves out and mark which cylinder they were in. You can clean the head either with a parts washer or by soaking it in a big container of red devil lye (wear gloves) for a week or two. It should come out brand spanking clean. Once it is clean take a machinist's straight edge and check it for warpage, or take it to a machine shop and have them do it. Use a dial gauge and check all the valve guides for runout. If the valve guides are bad you will want to have new guides and valve seats installed. Also check for cracks. If there are no cracks and the valve guides are ok put new stem seals in and put it back together. Lap each valve/seat combo until the seat has a nice even matte gray color.
Then put it all back together and fire it up.
One thing that you may notice is that the 1948 head has smaller spark plug bores. These spark plugs are 10mm and are harder to find, but they work just fine. I had a '50 block with a '47 head on it in my truck and it ran good before I killed a rod bearing.
