I'm thinking that it really is one of the Dorsetts, which were very common, and there are still quite a few of them around.
They were mostly from the at 1950's and 1960's, as I remember. I see them in the classifieds and on Craig's List all the time. Must be reasonably durable.
The pilothouse looks homemade. I don't recall seeing one that large, either.
I'd look it over very carefully for workmanship and structural integrity at that age, and particularly at the pilothouse.
The I/O's can be a lot of cost to repair when they get old. The I/O unit is on the order of $4000+labor to completely replace, and anything other than a water pump and a lubricant replacement will run $800-$1500.
Older boats with I/O's are often abandoned to the scrap yard when the cost of the I/O repair or replacement becomes excessive compared to the residual value of the boat. Outboards are much easier to renew or repower.
I've got two Mercruiser V-6 Alpha Ones in my Sea Ray, so I've lived with the apprehension of the I/O repair costs, and have incurred them three times.
The I/O drives are a interesting solution to the power choice problem, but are complex, have their own problems, often don't age well , and can be very expensive to work on.
Be sure they've been serviced well. If you're unfamiliar with them, have someone who is ride with you on the sea trial and listen to them and check them out. A professional mechanic would be my choice. A pro can hear and spot problems that will cost you later. Often people dump these boats when they know trouble's coming.
I really don't want to be so negative, but feel the warning is only appropriate, as I've BTDT!
Good Luck!
Joe. :teeth :thup