[KenB]

Those are giant lawnmower motors. I had a 115 on my mako17 that I did a lot of work on myself. Find someone you trust to call for advice and also buy the service manual. You can get most parts super cheap at NAPA. Obviously, there are many fixes on those motors that will take a good shop, but for example you can do the oil/premix conversion yourself in under an hour. The whole point of running twins is that if one craps out you can get home on the other.

I am sure this guy is a solid guy and not a fraud (there are lot's of frauds out there in the used engine world) but he has to make a buck. His prices sound right, but that seems to be a lot of work for old motors (that are generally thought to be pretty bullet proof). On the other hand, if you give this guy your business, there is the off chance that he will do right by you and take care of you in the future (or he might keep gouging you because you are an easy mark... I have experienced both. There is a horror story of my buddy going in and asking for a $100 fuel pump to be replaced. When he came back, they did the whole prop/paint thing and wanted $1000, with $600 for labor on a $300 motor. He gave them $100 and got his old parts back, but had to throw a nutty in the shop.)

I personally would not spend 4-5K on 20 year old motors. BUT expect to be shelling out almost twice that by the time you get done trying to replace with even a used 4s. I wouldn't do more than oil changes on a 4s, especially if you can find an EFI/computer one. If that one engine is shot, finding a replacement head should be much cheaper than fixing the current one, but not if you pay someone else to do it.