That is a standard Merc inline four engine. If it really is a a '77 it will have 4 ignition coils. The design is fine, the condition at this time is what detemines it's goodness/badness. It is a 31 year old engine!
All the Merc 4/6 cylinder Inlines were basically the same. They had the same basic parts, with some minor differences. The 3 cylinder inlines were also similar, but with two carbs/ 3 cylinders
