Measure the dimensions of whatever you think may fit and make up a little mock unit with carbboard and tape, then see if you can angle it in there before you buy.
Some manucfacturers websites have the detail drawings too, otherwise take a ruler and pad into store and measure all the dimensions, just say what you are doing, if it's locked down ask them to unlock it and place it on their counter.
I have no shame when going into store with ruler in hand, even though they are thinking I want to run out the store with it on the unlocking request so I let them stand right there staring at me for the entire process.