Ask if they have a profile sweep of the units - something you can print out and test on your rims.
example of the Harrop one here: https://www.harrop.com.au/shop/system/download/PROF_SWEPT_CALIPERS_FRT_BA_FG_ULTIMATE.pdf
Also ask if they require any other hardware to fit (adapters, brackets, lines etc) or if the standard hardware and plumbing bolt straight up.