I need a new rear mech.....

.... and I'm skint. So I am planning on putting an Apex long cage on with a sram pg1050 11-32 cassette. This oughta work with my otherwise sram Rival setup, yeah? Also, having a long cage mech shouldn't matter if I go back down to an 11-25 should it? (I do have an ulterior motive here, I need to beat a mate up Mow Cop)

Thanks!