One of your countrymen
posted a similar question here recently, and this was my response:
"Most of the riders on this Forum live in North America, Britain, or Australia, and I believe none of these places import the 350 Twin Spark without the electric start. In fact, the USA has imported no 350s at all since the 1990s, and only then very few of the old "Iron Cylinder" type. Accordingly, I doubt anyone here will have the expertise you describe.
You might have better luck posting your question to a good Indian forum like
https://www.team-bhp.com/forum/, where someone may have the experience you seek."
I suspect that in the end it might be easier to swap in a fresh electric start engine than to modify your existing engine. Perhaps you could find one from a road damaged bike and then sell your original engine. Someone will want it.