Reversing a list without (append)
Given that you don't want to use append, this looks great to me. I'm not sure if I can even think of a different way to do it.

My only suggestion would be naming related. l is a terrible name for a variable - it's too close to 1. orig is questionable, since it's not really the original list, it's the list you're currently "popping" (logically, not literally) off of - so you could simply rename both l and orig to something like lst or xs or elems or ....