From an expert on the matter:
Thanks for the email.
Yes, that's the Scientific Torpedo model boat and it is from the 1950's. This was a model kit and, from what I can tell, it was sold mostly through hobby stores, toy stores and most frequently through magazines like Popular Mechanics. They are not terribly rare but hard to find in good shape or in not built up shape. In Bill Arick's book there is a great two color ad (red and white) that has a price of $2.50! Pretty neat, eh? The motor show on it is an Allyn Sea Fury with a small caption that they also sell Atwood gas outboards.
The motors on the boats I've seen pictures of, or through old ads, lends me to believe that most people put the gas outboards on them. Usually an Allyn Sea Fury, an Atwood, or a Wen-Mac gas motor on it. These motors were all self contained, meaning that the gas tank was right on the motor, so you didn't have to have anything in the boat hooked up to the motor. The problem with those motors from your point of view would be that they look like an outboard motor but not like any real motor made by a big manufacturer. If you ever intended on running the motor, they are very cantankerous! Hard to start, hard to keep running, tricky needle valve adjustments, lots of special tools, etc.
I would suggest you get a K&O motor for it. It would still be the correct size and mount right on it. Since it's a hydroplane my suggestion would be to find a K&O 1955 to 1957 Mercury Mark 55. The bigger Mark 75 and 78 motors would look cool on it but they are very expensive and might overpower the look of the boat. If you wanted to run the Mark 55 it would be easy to just install a very cheap battery box from Radio Shack, hook up the wires and go.
To buy one of these motors can be expensive. Two choices there. One is Ebay, of course. The other is to call Bill Arick who would have one for sale. At least with Bill you'll know that the motor runs correctly and he usually has nice motors to sell. He doesn't have an email address so you would have to call him at: 316-755-1528. Ask him about his new Toy Boat book, I think he sells for $49, which has that picture of your boat in it.
Oh, what the heck. I just scanned the picture from the book. Here it is attached. Notice, there are only gas motors in the ad. I still would use a K&O, though, for realism.
I hope this helps you. When you find a motor let me know and send me a picture of it on the boat. Would love to see it.
Hope all is well,