Do you have to know the exact Displacement or just 100% verify that it has been stroked?

Assuming the motor is out of the car and you can put the deck horizontal to the floor/tabe....just get a piston to BDC and pull a plug and keep putting a measurable volume of Marvel mystery oil (or some other light motor oil) compatible fluid into it. allowing some measurable displacement for the distance between the deck height, the head gacsket thickness and the approx distance between the head deck surface and the bottom of the spark plug hole, you can get pretty close. Of course your gonna be off by a bit for combustion chamber and piston eyebrows/dish/dome, but if you just want to do it quick and dirty that will work for a rough guess. A .030 over zero deck 440 would be about 913 ccs (just a little over a quart) plus whatever the make up distance (i mention above would be) is .

so a 4.15 stroke would already take over a litre (a couple ounces more than a quart) to fill just to the deck height. That (conveniently) seems pretty easy to determine.

To empty it, make some sort of nozzle that screws into the spark plug hole and run it through a hose and turn the crank.