Sure you can! Well, maybe. You should have a Saginaw steering box. Is it tight around the box, or is there a bit of room (about 2" between existing steering box and engine)? It there's some room, you can bolt a Saginaw power steering box in it's place. You'll need to drill a couple holes in the left frame rail, and you'll need to cut the steering shaft off and weld an end on to bolt to the power steering box "rag" joint. This is easier than it sounds. If there's room for the power box it's not to difficult. You'll have to fab a bracket for the PS pump, but that shouldn't be to hard.
I did this on a 63 Rambler, but I swapped a newer engine in that had a PS pump. What engine does your Jeepster have -- the F-head four or the 226 L-head six? Or has it had an engine swap?