Not to mention a diamond blade spinning at 13k rpm's a foot or so from my head.
A 9" blade won't work in the close quarters. I had a long grit blade for cutting cast iron which I had used on a 4" pipe before but it was hitting the joists. I might be able to find a shorter version.
When I bought my house it had a hot water radiator system which had been left full of water at 25 degrees below zero. There were lots of broken fittings and radiators. It had black iron threaded pipes but cast iron fittings. I found that the easiest way to get sections out for repair was to use a chisel and sledge on the cast iron joints. Usually I could bust a joint in no more than three blows even laying on my back and hitting above my head in the crawl space. I'd then replace the cast fittings and put a union in the pipe run.