I'd doubt you're going to get seamless switching between the two wheels even if the cassettes were the same unless the wheels are identical in every aspect as the freehub will probably be positioned a little differently. I could be very wrong though. Or you might just get lucky. Might need a slightly longer chain too.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"