I've only ever seen the likes of Eibach that go -40mm. As you say, coilovers are the best way to get 60mm low. With a drop of that much, you'll probably need to cut the inner front arch away at the top (the same as how FRP's are) otherwise you'll rub. Especially if you're running 17" wheels (7" wide) You'll also get inner tyre wear as there is no adjustable camber on a Puma unless you get adjustable lower arms.