The 1.6L is a Ford Industrial industrial model and as I recall takes a starter specifically to that model and is mounted on the opposite side of the same engine found in the pintos and capris of the day. The parts book lists the original starter as a Lucas L.H. mount(exhaust side) P/N 71BB-11000-EA and then in the parts breakdown for the starter the following starters are listed: Lucas 75AB-11000-AA and -BA.
When I first bought my Bombi, which was also my first snowcat, I found it was a mixed match of original engine parts and parts bought from Napa for the 1.6L put into Pintos. I had all sorts of performance issues and then found out the difference between the Pinto engines and the industrial engines put into the Bombi. At the time there was an industrial ford parts dealer where I lived and he helped me get all the correct parts like carb, distributor, starter and manuals. With the correct parts the engine was very reliable and had good performance.
I would either take your old starter into a rebuild shop that specializes in rebuilding electrical components or hunt down a ford industrial parts dealer and see if a new application exists. Lucas products have a poor reputation so another manufacturer would be a blessing. BTW the model of the Industrial 1.6L is: KSG-416