I pulled it out about a month ago and realized the vintage screw collars only allowed for about an inch of loadable "sleeve." I debated whether to buy new collars and lost interest. In the past few days, I decided to resurrect the project and bought a couple of 1 inch bore zinc plated mild steel set screw collars for $1.95 each. I then grabbed the bar to evaluate the existing collars and overall condition. It was pretty beat up and I wish I would have taken a before picture. The existing inner collars were rusted on, with one side having a set screw and the other side no set screw (they are of course different collars). I soaked both ends in vinegar and was able to disassemble it, then I removed the electrical tape and then removed the athletic tape that was below that. Finally I scrubbed it for a while with the vinegar solution and the next day with brake cleaner to finally have a mostly residue free hollow curl bar with no knurling. Now I know why all of the tape was there.
The collars are supposed to arrive June 16 and if I am successful, I will play around with it and possibly order some spring clips. I hate to put money into this as I can get a brand new curl bar with knurling, plenty of loadable sleeve and spring clips for $40, but I am willing to throw another few bucks at it along with some elbow grease.
June 17, 2020 - Update
The collars arrived, but were too small. My decision to go with a new Marcy EZ Curl Bar from Big Five Sporting Goods for $39.99 is all but decided.