there are data on "coulpling".
i know nothing about it. if you're just looking to get your speakers aimed up a little towards you, no problem. you can use phone books if you want. use a chair, milk crate or a purpose built amp stand; there are lots available. just make sure everything is stable and doesn't make unnecessary rattles. some combos and cabinets have "kickback" legs or are built as wedges. sometimes just elevating the amp or cab works fine and there's not really a need for angling it.
"In the land of the blind the one-eyed man is king"
Soundgear Club #34 Genz Benz Club #426 Low Watt Tubester #6