I have had a Clausing 5914 lathe since 1985. It came with the Royal lever collet closer and 5C adapter that fits in the spindle internal taper. The spindle ID is large enough to allow a 5C draw bar, a feature that some 12" lathes lack.
I also have a Pratt Burnerd KC15 collet chuck and collet set with 1.5" capacity that fits on the L00 spindle that I got soon after the lathe. The extra capacity (over 5C) allowed one paying job that paid for the chuck. Much more recently, I mounted a Sjogren 2J handwheel collet chuck with 1.38" capacity on an L00 adapter. Then I mounted a Pratt Burnerd KC25 collet chuck with 2.5" capacity on an L00 adapter. I got the collets for both those chucks many years before I got the chucks and mounted them. These were all used chucks and it took years to find them and their collets. They cost thousands to buy new decades ago and more now if still available, so I had to wait as long as it took to find them at prices I could afford.
All three of my collet chucks hang off the spindle nose, so they sacrifice some rigidity and length to the tailstock or turret, but they are very accurate and great for large precision work. The 5C adapter inside the spindle is short and much preferred for both smaller and production work.
I have a Jacobs 900 Rubberflex lever-actuated chuck, but have never adapted the lever linkage to the lathe.
At one time, I had a spare 5C sleeve and ejecting collar for the Clausing. I can't recall if I still have them.
Larry