I will give this a try, even though your description does not correlate with the carbs on my two '79 Model 7s or my shop manual.
As far as I know, there are only 2 types of choke. One is a mechanism which blocks the air intake to the carb with a flap or shutter, creating increased vacuum in the venturi and increased gas flow through the main jet. The other is an extra passage for fuel to flow into the venturi when opened by raising a sealing plug from the starting fuel supply.
My carbs and I think yours, are of the second type, however, I have never seen one of these operated by a cable which enters the carb fro the bottom. They are usually controlled by a cable which enters the top of the carb, just to one side of the throttle slide.
Look carefully at the parts you have. The hole into which they fit, should have a raised "seat" around a hole in the bottom of it. The brass slug should have a rubber insert in one end of it with a matching indent caused by pressing on the seat. This piece goes in the hole first, rubber end first. The spring normally seats in the outer end of this slug to apply pressure for sealing when the choke is off. You have me on the plastic piece, it could be an alignment piece for the top of the spring but unless someone else posts, you may have to figure this out by figuring out where it fits best. This assembly is then held in place by the top of the carb.
Your fuel leak is most likely caused by the needle and seat vontrolled by the float. Make sure that the float does not have a leak (fuel inside it), that the pointed end of the float shaft and the seat in the top of the carb are clean and in good shape and that you install the float with the pointed end up. Sorry about that last obvious one, but apparently, several people who post here have had that problem.
If you stop the fuel leak, you will neeed to fix the choke to start it. You should be able to make a cable from a 10 speed gear change cable.