If you're working with used batteries, you'll also definitely want some way to measure the capacity of them. You could build some kind of test rig to cycle them and measure their output (at some meaningful load, say 50A minimum, just as a rough starting point).
Something like this, but with a higher amp draw:
Easy Test of Battery Amp-Hours Capacity
I don't know how often your usable cores come available, but it may take you a bit of time to sort through them to evaluate/put together a pack that will be serviceable in a short-range EV.