It's always a good idea to keep the lifters in the same order on any cam, but flat tappet cams, both hyd. and solid must have the lifters stay on the same lobes. If you mix them up after the cam is broken in, there's a good chance the cam will go flat. Dosen't matter if you swap them from engine to engine, just keep the lifters in order. On roller cams it really dosen't matter.