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I thing the O/A with an intense, narrow, hot flame on a cutting tip (obviously don't touch the oxygen lever) would be the way to go. Smaller propane/MAP torches are pretty lousy for getting parts apart: Even though most of them might be able to get the metal hot enough (eventially), their colder flames they take a lot longer to get the parts up to temp: By the time you've expanded the one part, the heat has conducted its way though to the other parts so they've expanded at nearly the same rate. You need the lots of heat to be applied fast, so the one part expands on its own before too much of the heat can conduct to the mating part. It also helps making sure you don't damage other nearby parts from too much heat. It sounds counter-intuitive, but the hotter flame keeps other parts cooler/safer. Better to heat in one quick shot with a hot torch before the heat can conduct to other parts. We used to get that with camera heads that came into the machine shop for repair. There was one Italian company where you had to heat an aluminum brake part stupidly hot to get it out. We'd get lots of units in where the internals/electronics had been melted or ruined, because people where trying to use small torches to prevent damage to the fancy electronics parts inside. They'd get shocked when they'd see us bring an super-intense O/A flame into a small, precision piece of equipment with lots of fancy electronics. But the brake has to be heated crazily hot to get it apart, regardless of how you heat it. If you use a colder flame from a handheld torch, by the time the brake gets up to temperature everything else has heated and melted. But if you use an intense, narrow O/A flame, you can get the brake up to temp, get it apart, and cool everything back off with an air gun before the other parts even know what's happening (sort of speak).
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