I had a MERC 190E model 92 W124 series( sold it last month ) also fuel injected and I converted it to CNG, The kit was Landi Renzo and I had the work done from Walton Road. I dont have the number of the workshop, but here is my number call me and I will tell you where the workshop is.
These guys used to work for GASOLINE PAK ( Quite a big CNG workshop is Township )and just started there own shop at Walton Road and they are quite good.
my number is 0300-4120254