Yes it can be done & I have seen a Diesel on CNG in Pakistan Lahore done by FTFS Faisal Town Filling Station CNG conversions. But there is a problem.
You cant have it operating on Dual Fuel like Petrol engines. Once it gets converted on CNG you cant run it on Diesel.
In the end I take it as my resposibility to advise U not to go for CNG, as it has a limited future.
Dont do this to ur car.
TC