20X24 would be near or maybe even beyond the height capability of the 23C. Crank it all the way up, focus, and see if the image is big enough to fill the paper. An easel for 20X24 would probably have to be home built, but that needn't be too complicated. Exposure time increases in proportion to area plus an adjustment for reciprocity failure, so you may be facing very long exposures. Sink space is usually the greatest problem with big enlargements. 16X20 can be handled in trays in many darkrooms and in rotary processing tubes just about anywhere. 20X24 gets difficult, but you can probably build a suitable tube and some rig to rotate it on (hand power is possible). With bigger paper, handling time increases, and that causes some additional problems. Particularly with tubes, you may need to dilute the developer to get longer processing times, Or you could select a slow developer. Having the extra time will reduce splotches and irregularities that may occur while changing solutions. You will have to test to determine development times and how dilution affects contrast. Big prints require more solution, too.