Ben,
I am sorry I don't know anything about that photo. I keep an eye out for Egli photos on the internet and that one looked interesting. I try and trace them if I can, but many have no info.
This is one that shows the same frame, but it has a closed loop at the rear.
The gussets are often used to mount sheet metal covers, tool and battery boxes.
Your forks are Metal Profile, I believe. Cyril also used oval tubing for the swing arm. It is called oval, but it is a rectangle with a half round top and bottom. I should say that assuming Cyril built it he would have built it to the owners spec. He could add gussets and a loop in the back.
When I spoke to Cyril in 2009 at Bonneville he told me he had built 50 or more Comet frames. So, most of these Egli- Comets would have been built by Cyril. It the photo above, that is a fuel tank that Cyril sold. Cyril worked under the name "CTG" and you may spot that somewhere.
As Greg said the front brake is a Grimeca, which is an italian manufactured brake, but it has been available on Eglis since the late 1960's.
I will try and describe how the oil lines work. There should be a pipe or line coming down from the back of the oil tank that is called the feed line. This line goes into a banjo bolt that goes straight up into the front of the oil pump under the engine on the timing side. The oil pump pushes this oil into the filter chamber, the one with the big hex cap under the mag on the primary side. Now, go back to the timing side. That silver banjo bolt under the breather goes directly into the filter chamber. It takes the filtered oil and feeds it through the timing cover to the crank (that is the crank quill on the timing chest directly back from that banjo. This oil also goes to the cam and to the cylinder bottom. That's it. That takes care of the feed side of the oil pump.
All that oil flows into the sump that you have been draining. The flywheel, when turning, pushes that oil into a chamber at the back corner of the engine. There is another banjo bolt down under the engine. The oil feed pipe goes right by it. This is the scavenge oil pipe. All that oil in the sump gets pushed up this line that goes by the rockers and drops oil into them on its way to the bottom of your oil tank. So, this lubes the rockers and is the return line to the oil tank. It may be on the front of your oil tank.
When I want to drain the oil out of the oil tank I usually undo the ring clamps that hold my rubber oil line onto the banjo. This is that banjo bolt underneath that is near the front. You can undo the banjo itself and drain the oil, but I usually use the ring clamps because I am too cheap to keep replacing the seal on the banjo bolt. Either is fine. As you know, you also have to drain any oil that did not get pumped out of the sump. You can undo the big hex cap on the oil filter chamber, but you should order the tool from the Club if you did not get one with the bike.
If you put in a new filter you can do up the big hex cap (no goop necessary) and then go to the timing side. Undo that banjo under the breather and use an oil can that squirts oil to fill the oil chamber. If someone is helping he can hold the bike off the stand and lean it to the left while you fill the chamber. Remember, you have to put the nozzle of the squirter past the timing chest and go right into the oil chamber or the oil you are squirting in will just drop to the bottom of the timing chest.
Starting at bottom right, Oil banjo straight up is the feed from the tank, to the bottom left is the scavenge from the sump that goes up to the head and then returns to the tank. Above the scavenge is the cank shaft quill supplying oil to the crank and top right is the oil chamber banjo bolt where you can prime the oil chamber if you empty it.
David