I remember old school engines, and earlier boat set-ups from the 70's and 80's had had water jackets installed around the cylinder, and were started with a belt/pulley on the front of the crank(where it joins the prop-shaft). Although it's not on the "back" of the engine, it still was a popular way of starting these things. The belt just stays in the boat, as it falls free from the crank once the engine is started. Similar to what I've seen on RC heli's... Matter of fact, I just saw an old club member use one a few months back on his boat at one of our float-fly events. Most starters with aluminum cones have a belt-drive-groove machined in for just such applications.
You might use Google search to see if any of those components are still available(new or used), and you might be surprised at what you find. If nothing else you might get pics to go by if you're planning to fabricate components. Something tells me there's something out there though, but I'll leave the searching to you. Good luck with it.
Last edited by DGrant; 06-23-2018 at 07:10 AM.
Reason: added info.