Noman Bhai, Firstly, best of luck for the project!
I am not very familiar with modifications on Suzuki jeeps, but I would think that getting the jimny engine and gearbox would be a good move and a clean modification. This is a very small jeep and frame, so you have to keep things in balance. I am also not familiar with the 1N but to go from 550cc petrol to 1500cc diesel seems like a big jump. I also read something on the SSR gear, which probably would be overkill here as it is heavy stuff even in its lighter shapes.
You should also run the mechanical plan by Nikku Ustad as he is widely regarded as the modification guru at Citi Sadar Road.