I'm wondering what you mean when you say the distributor cap "broke off." From the looks of your pictures and your description it sounds like the big wire that holds the distributor cap on just slipped off and the cap came loose. Why don't you just try putting the cap back on and pull the wire up tight to hold it on and try it again. (In your picture it looks like the wire is above the distributor. I don't know how you'd get it to slide over the distributor cap from there. I think you need to hang it below the distributor, put the cap on seated down tight in the right place - with the tab in the slot, then pull the wire up over the cap to hold it on.) I'm thinking that it will probably work just fine. If not, let us know for more ideas.
Here's looking up from under the car at the distributor cap to see how the wire is pulled up and over the distributor cap to the middle of it to hold it on.