Regarding your CNG question, I have first hand experience. My overall opinion is that for daily driving, unless you own an oil well or something, you have to install CNG. Bear the following in mind:
1- The weight distribution of your vehicle will be changed significantly enough to effect offroading. You will need to install at least two tanks, and large ones, like 50 kg tanks to get it to be worth switching over to CNG.
2- Becuase these cars run on a carb and are not EFI, CNG tuning will be difficult. You need to increase timing significantly, advance it. When you do, the performance on Petrol drops. Finding the right setting is going to take you time. These cars, for some reason, behave very differently when there is no CNG installed at all, you will be messing with timing settings every other week.
3- Having said that, mileage on CNG is going to be horrible also.
I keep switching from keeping my tanks in the RKR to taking them out, and messing with overall settings all the time. It pisses me off frankly, so 80% of the time, I just drive it on petrol. Also keep in mind that CNG will dry the butterflies of your carb quickly, you will need to reset your carb about 2-3 times a year, DO NOT ATTEMPT THIS WITHOUT HAVING THE RIGHT CARB MECHANIC.