I would start with a spark check; see if it will consistently produce a bright white spark that will jump a 1/4″ gap. The cracks are of course a very bad sign. The coils will need to be replaced at some point even if they seem to work now….but they might last long enough to allow you to evaluate the running quality of the engine. New coils are expensive; better to know that the engine is worthy of that first.
There are surplus military coils that some people have successfully modified. The connection for the spark plug wire is in the wrong place….and it needs to be soldered. They currently can be had for under $20.00 on ebay. The last time I looked; oldmercs.com had the “correct” coils for $80.00.
