I would suggest you give up on the C&V forum for now. I mean, we're always happy to have you here, but what you need now is the folks over at the Folding Bikes forum.

In a nutshell, the Raleigh Twenty is a fine bike but a poor folding bike. The ones with 20 x 1 3/8" wheels are all steel, the ones with the 20 x 1.75" wheels are all steel except for the insanely long Weinmann sidepull brakes. To make one light, you pretty much have to replace every component on it, which will run you into a lot of money and in the end you'll have a bike that cost a lot but still doesn't fold well.

Also, as for upgrading a Twenty, note the setup of the handlebar on most modern folding bikes: it has a hinge just above the headset, offset by about 45 degrees to one side or the other, so when it folds the whole handlebar flops into a position that's upside down and turned at a right angle, so parallel to the wheels and either between the wheels of on one side of the wheels. This folding stem comes with just about every modern folding bike, but is nearly impossible to buy after market. You probably can't get one for a Twenty.

Bottom line, I would suggest you research folding bikes and get a modern one. I ride a lot on vintage bikes and I commute on a folding bike every day, but there's no way I'm ever going to commute on a vintage folding bike.