Both my Vins were without the chain oiler pipe for some time, and I simply turned the screw in the oil filler to close the opening. Never needed to cap off the fitting at the rear of the UFM. The float bowl nut does come in handy if the auto cutoff valve in the oil supply line doesn't quite close off the flow after you've removed the main oil line when working on the bike and removing the UFM.
Hey Charlie, my Comet it almost back together after having a new piston, cylinder, and muff installed. Should be able to go riding with you soon.