As far as I know, Schwinn never sold these tall bars.
They were in the catalogs of stores like Montgomery Wards, Sears, and Kmart. I have a few catalog page scans, that I can dig up.
They almost all mount with the flattened bottom ends with three holes, like a very early Persons bar but not like a later Schwinn bar.
The "shock" setup like GSC has, is exclusive to the Krates. Nice adaptation of that thing btw.
There were some variations at the top seat mounts- some Columbias used bar clamps up top, with a bolt to a tab on the seat. So to change height, you loosen the top screws and slide the whole seat up and down the sissy bar- no cross drilled holes, just round bar the entire length of the thing.
Good luck finding one that is in good shape at a reasonable price though.
--Rob