I am not aware of any production change to the 97 vs pre-97 re. the head gasket.
First, the RIGHT side of the engine is the passengers side. The 2 common areas for a 104 head gasket leak is the right rear corner and right front HOWEVER if the front cylinder head cover "lip" seal leaks, it is difficult to distinguish from the right front corner of the head gasket itself leaking. The tech has to be very careful to clean, drive, and reexamine the area if the leak is right front. The front cover is much cheaper to reseal than doing the whole head gasket. 1/2 the time, with a front engine oil leak, the front cover just needs resealing.
With the 104, a failed head gasket will usually just oil externally, no mixing of oil and coolant. The decision to do the job is up to you, how much leakage can you stand?
It seems like if you are going to have a leaking head gasket or front cover, it'll do it around 75,000-125,000 mile range.
The 722.6 did have several modifications done to it in production. It seems like if they were going to fail, they would do it rather soon. If yours has alot of miles on it, I wouldn't sweat it too much. To update some of these parts is horrendously expensive for both parts and labor.
One thing that is fairly common in the 722.6 is called the conductor plate, it contains the temp sensor and more importantly 2 speed sensors. if one of these fail it will lead to the tranny going into limp-home mode. It mounts to the top of the valve body. I don't believe there was a significant change made to the valve bodies since the 722.6 came out, but there were some other changes made.