Model engines do not have a high parts count so some people think they are simple.

but you are looking at about 75 yrs of evolution by a lot of engineeers and mechanics. The materials are very select and the tolorances are close.

Once you get the hang of changing bearings it is not too bad.

There are a lot of people in this forum that know how to do it.

You are going to need a way to heat up parts of the engine and you will need a gear puller to get the prop drive hub off.

Also needed are feeler gages to set the valve clearance and metric hex key type wrenches or Allen wrenches.