Would It be alright to hook up the CNG fumigation carb/nozzle/else before the air cleaner? The problem is that the air filter is part of the plenum. There are 4 individual runners that run from it to the engine. So unless I put on four individual CNG nozzles after the air filter I can't add natural gas fumigation after the air cleaner. So for practical reasons it would be easier to just add natural gas before the diesel's air cleaner.
Here's a VW MK2 diesel air filter:
VW VOLKSWAGEN 85-91 GOLF / JETTA DIESEL 1.6 Non-Turbo AIR CLEANER AIR BOX | eBay
Another idea would be to adapt an air intake off of a gasoline, perhaps carbureted VW and wire the throttle open. That way I could replace or modify the carb to something that can fumigate the natural gas into the intake.
Another thing I'm thinking is I could put on a K&N air cleaner on the beginning of the intake and put the CNG fumigation after it. Maybe the second air filter could be left since the natural gas is a gas and should flow through the paper filter element? Or I could cut out the paper element and use a filter's gasket and use the K&N air filter for the only filtering.