Is a power hammer realistic if I've got no shop and no 3 phase?

Ran a 50 lb hammer off a residential panel for six years, so yes, it's doable. The motor on most old hammers that size is only a couple horsepower, which at 240 volts is in the ballpark of 10 to 15 amps depending on the motor. A standard 30 amp garage circuit handles that fine. The starting surge is the thing to watch, but a rotary phase converter softens that somewhat, and honestly the motor starting under no load, which is how most of these clutches work, isn't the brutal start a loaded compressor is. Your panel won't trip every cycle unless the breaker's allready marginal or undersized.

Seconding what was said about the panel, same story here. My hammer came out of a closed down farrier shop and lived under a pole barn tarp for two winters before I got it. Cleaned the old grease out of the bearings, repacked them, and it's been fine. Biggest surprise for me was the foundation, I just poured a thick slab with rebar in it and bolted the hammer down, no special isolation needed at that size. Go look at it, if the dies are still in decent shape and the clutch grabs, that barn sitting matters less than you'd think.

Barn hammers are usally not as bad as they look. Rust on the outside means nothing, it's the die area and the spring you care about. Bring a ball peen and tap the frame all around, a crack rings diffrent than solid cast iron, my grandfather taught me that trick checking out old line shaft equipment. Check the clutch leather or lining for oil soak, look at the die dovetails for mushrooming, and spin the wheel by hand to feel for tight spots in the bearings. Ask him to let you run it if the motor's wired, even a minute under no load tells you plenty.

Update: went and looked at it yesterday. Brought a ball peen and tapped around the frame like was suggested, all sounded solid, and the dies look barely used. Bearing grease was old but not cooked. Panel question put my mind at ease too, sounds like my garage circuit can handle it. Talked him down a bit and it's mine, pickup next weekend.