Can the oil filler from the D jet system be used with an L jet system as long as i run the vacuum hose to the intake elbow like it is on the l jet?

My vote is yes. Although I've never done it. This port is just the crankcase vapor line. It should work either way.

It will work but I don't think that came from a 1.8. AFAIK 1.8 don't have a breather port.

Not sure if the djet oil filler has the extra oring that is required to ensure you have no vacuum leak from the cap.

The cap vent (labelled L-Jet in your pic) has a spring loaded check valve in it. The piece labelled D-Jet doesn't have that valve. I've seen that 'D-Jet' unit before plenty of times, but I'm actually not 100% sure what it came from. The early (70-74) units have a simple hole in the steel portion which has a plastic PCV valve mounted to it. This is the setup that most D-Jet users have in their cars.

That is the late 75-76 D-jet oil filler. No PCV. I have one on my car. It has a hose that runs to the airbox above the air filter. It could probably be made to work with the L-jet depending on how you hooked everything up.