"But...
Can I get a pipe cutter, cut the closet bend before the 90 degree turn
and
use one of those sleeve and clamp devices? "

Yes, but it's a special pipe cutter for cutting cast iron. You can
rent one. It's essentially a chain with a small sharp blade at one
point that gets wrapped around the pipe. You then tighten the chain
until the blade causes it to snap and break.