I will echo the sentiments on the Chrysler outboard. They fall somewhere between suck and blow. They could never get the carburetion right and they always run depressingly lean.... if they run.
If you're going old boat and want to avoid some possible pitfalls, look for aluminum. It can't rot. Having said that, you'll find that many fiberglass boats are much more appealing to look at and the ride is often better. Aluminum doesn't bend in multiple planes, so they are kinda limited to simple curved hulls, whereas fiberglass can be any shape you want. The problem with fiberglass boats is that they're almost always a wood core with glass over it. Years of flexing and bending causes hairline cracks which means there is a fair chance an old boat will be rotten.
In truth, that's not always a bad thing. Of course you would prefer to have a not-rotten core, but the boat I'm running this summer is a 1968 Glassmaster, 15', 70hp, and that boat has been absolutely abused. The whole family lives on a lake in the summer, and we often travel to the ocean. That boat has seen nearly 60 years of salt and fresh water, and honestly used three times a day for hours at a time. It has had cracks in the gelcoat for 20 years, and just last week my foot went through a rotten spot in the raised floor. Don't care. Transom is still good. I covered the hole with a piece of plywood and kept going.
Some glass boats get super flimsy when the core rots. Some don't. Wood is cheap, but glass is expensive, so some manufacturers use a thick wood core and a thin layer of glass. Others will use just enough wood (think like luan) to basically be there for the glass to stick to, so if that core rots, it really makes little difference in the integrity of the boat.
I will also ask an indelicate question... how, um, "mobile" are you? You mentioned grandkids. Those bubble windshields are an absolute nightmare if you ever want to do a shore landing. Dock, fine. Beach, not so much. My 57 Sea King windshield lasted about 4 years until I had enough and I took it off. On the other hand, the (very lovely) runabout that MTN pictured is much like my Sea King. Easy in/out, but if you're out on the lake and a rain shower kicks up, or it's a chilly evening and the bugs are out, you're getting pelted in the face.
If the grandkids are still young, freeboard height is a thing to prevent them from falling in.
Any of the bigger-name old outboards are a good bet. OMC, Mercury. If you get old enough on the OMC that it has the dual fuel lines (early 60s-ish) from the tank, you will likely find that parts are hard to get. I do have a 62 or 63 Evinrude 10 and a 68 Evinrude 6 that refuse to die. There is truth to "they don't build em like they used to," but you also will find that they are much heavier for the power you get.
Also, be aware that in the early to mid 80s, manufacturers started rating power at the prop. Previously they were measured at the flywheel, so a 35hp from the 70s has about 15-20% less power than a 35 from the 90s. Size accordingly.
I think you'll find that cheap boats aren't the expensive free porsche you're expecting. The old saying of Bring Out Another Thousand is for people with a nice I/O cruiser that drop it off at the marina in September for an oil change, storage, and winterization. If you do your own work, boats are some of the cheapest and easiest things to own. A 2-stroke outboard is usually bulletproof and needs almost zero maintenance except for a possible water pump. People will mock me for this, but the 1988 Merc 70 I have on the glassmaster (the one that has been abused forever) has had one water pump replacement, and that was only because I had to pull the lower unit for a seal and I figured it was a good time for preventative measures.
The best boat I ever owned (and still do) was a $1200 Baja 19' I/O with a seized 305 and motor stringers so rotten that they had grass growing in them. Stripped it to a bare hull, built a 350, found a good used gimbal that let me put a newer Alpha outdrive on it, and added a rear seat from a Dodge Dakota extended cab that I covered in vinyl. 65 mph for $3600 and my own labor, and I could get my money back for it easily.