I dealt with this a couple of years ago. Got a Unisaw down my basement
steps. We removed the cast-iron top. It comes right off with 4 large
bolts, one in each corner. This not only gets rid of a lot of weight, but
also gives you a few inches more clearance, and makes it less top-heavy.
Also took off the height and tilt adjustment knobs (for more clearance).

With the top off, me and a buddy got it down the stairs on a hand truck.
Putting it back together required re-aligning the top with the blade, but
that wasn't that hard.