For H.W. or HVAC heat or a N.G. Stove/Oven ?
Once you "Finish" deciding which CNG vendor to use for the Chassis Parts...
You can install an Electric High Pressure Compressor on your N.G. line in the
Carport or Garage that will "Fill" the H.P. CNG tank on the W126 overnight.
AT AN AVERAGE COST OF $0.85 per gallon (When compared with Petrol)
The only drawback is the OUTRAGEOUS retail cost of the Compressor, $4-5 K.
[The compressor is Italian,there are others]
http://www.ebay.com/itm/Phill-by-FuelMaker-CNG-Compressor-Refueling-Station-for-the-Home-New-/140727015413?pt=Motors_Automotive_Tools&hash=item20c3fbd7f5&vxp=mtr
Mercedes actually offers an E200 N.G.V. in the E.U. ...