if you have an engine that has linkage that runs from the carb to the timing ring, you have a mechanical advance ignition. If you do not have linkage, you have either a fixed or auto advance. The old brown box ignitions were usually mechanical advance.

I doubt the engine would have to come out of the plane. If there is access to the rear edge of the prop prop hub you probably have plenty of working room to make a change to an auto advance.

ALL engines are capable of adapting to auto advance ignitions. Some are just harder than others. Your Sachs likely has some type of Delrin (plastic/nylon) timing ring just over and behind the prop hub. That contains the hall sensor which would only need fixed in a non-movable position after establishing the advance to convert to auto advance. It really is quite simple but often sounds difficult. The only real issue is getting people to try something they have not done before. I did an ignition/sensor /timing change at a flying field for a kid last weekend. The only requirement to get the job done was a little time and a few small hand tools.

A pic of what you have would be most enlightening and permit further discussion for your assistance.