I have several doors areas framed out in my basement with the ceiling being low because of vents. In several of these areas doors will be installed. I am looking to install split jamb prehung interior doors but there is approximately only 1 to 1 1/2 inch of header to the ceiling. In other words the casing around the top of the door will not fit because of lack of space with the ceiling. Does anyone know of any short cuts that I can use to install the doors without it looking completely crazy. Can I cut the bottom left and right jamb to make the casing fit. This will leave a gap between the header jamb and the header. Can I insert some wood material to make work. Thanks in advance for any suggestion and advice.

Did you look into 78" prehung doors instead of 80"?
If you have 1 1/2" from the ceiling, with the 3/4" top jamb, that's 2 1/4". The same width as casing w/o any reveal. For the doors where you have 1" headers, cut the jambs, casing and bottom of the doors what you need to have a full head casing. I hope this answers your question in what your asking, if not let us know.

Thanks a million, this answers my question