B.Tech

Follow the link below for automobile engineering colleges in Pune and filter colleges which takes admission after Diploma.
https://www.shiksha.com/b-tech/colleges/b-tech-in-automobile-engineering-colleges-Pune.

Yes, medical checkup is compulsory for taking admission for B.Tech (Lateral Entry) in Marine Engineering
For more details check the link below:
https://www.shiksha.com/b-tech/course/b-tech-in-marine-engineering-lateral-entry-indian-maritime-university-chennai-mumbai-campus-meri-sewree-296923

The candidates should complete their B.Sc Degree under any registered University with subjects like Botany, Zoology, Chemistry, Biochemistry, Biotechnology and Microbiology. The marks of admission for this course may vary from University to University and in various colleges and Universities it cond

You require at least 70% marks in PCM for JEE Exams and mostly all colleges take that score.

Yes, you are eligible for that.

Chances are decent enough, depends on how you performed in GD-PI.