I'd been researching lots of info on this and finally decided to take the plunge myself. I'm a tinkerer

I got one of these for a pittance on Facebook Marketplace:



And one of these for about $20...



First issue I noticed was that the driveshaft coming off of the engine was too big. The shaft coupler on the Ted Williams is 3/4" (IIRC) and the driveshaft on the 190 was 7/8ths or maybe even larger.

So, I mounted the engine on a brace with the driveshaft coming through the bottom. And I grabbed my angle grinder.

Before:



After:



The top section of the driveshaft for the Ted Williams is a set screw at the top and a spline coupling on the bottom. You put the engine driveshaft on the Honda and then lower it on to the spline coupler. This then gives you a reference for how everything should line up.



Next was to make an adapter plate to mate the GCV to the Ted Williams top plate. I made the pattern out of plywood and drilled holes as necessary to fit everything up.



Once I had the pattern, I took it to the local high school metal shop. For a small donation, they used the plywood pattern to cut me an adapter plate out of 1/2" steel, which I brought home, primered, and painted. Once it was ready, I bolted it to the Ted Williams top plate.



Everything mated up perfectly and I bolted the engine down.



Next was making a throttle. I made a squeeze grip out of PVC and attached a cable running to the throttle of the engine...

https://streamable.com/o0wlsn

I also installed a low-speed stop to prevent the engine from dying when the revs came down. You can see it in the video when the throttle is released...there's a screw there that the throttle arm rests against. I had to move the spring to the bottom and attach a bracket to the bottom plate. But, everything worked.

Now it was time for testing.  I was worried that it would make my little Pond Prowler sit low in the back end, but it didn't. Total weight of the setup was only 47 lbs. Not bad for a 4 stroke 5hp motor...

And then, the moment of truth...

https://streamable.com/puj79m

It doesn't push the pond prowler so fast for a couple of reasons. One, insane amounts of transom flex, which I've since corrected with reinforcement. And the other was, the Ted Williams is a 20" shaft and the Pond Prowler really needs a 15" or so. I've fixed that too, by making a jack plate and moving the engine up 4" to reduce the effective shaft length by 4".

In the meantime, I decided to try it out on my lightly-loaded V-hull just to see how it would do...

https://streamable.com/stq5bs

I'm well under $200 for the whole setup, and I could definitely do it cheaper next time. All in all, a fun project and I ended up with something useful afterward.

That's neat and I have that same Ted Williams I think. Mines a 7.5 hp .  
 Been wanting to put it on my sears 10' aluminum flat bottom.

They're good motors from the standpoint of being fairly reliable and easy to work on. But, parts are getting scarce and a lot of them have the solid state ignition which is no longer being produced.