There have been a few threads on here regarding electrics.
As above, the big problem is the "fuel density".
As you have found - plenty of wee lightweight petrols out there. That 3.5Hp tohatsu has been around in various guises from 1 to 3.5Hp and I think has carried pretty much every Manufacturer;s livery at some point. (nerds feel free to correct me on the paint job comments!)
One thing to note - if you go for the super lightweight Johsorudes from the late 60s / early 70s (The ones with the open bottom case) beware if it's hanging on the back of your rib - the exposed plugs are fine if it spends the day pushing displacement craft around, the open bottom casing does however allow a lot of the spray from your main's leg into the HT leads at the spark plug so not a lot of starting then happens!