I cut the pipe! A friend underneath on one end of the hacksaw blade and me in the cupboard and we got it in half an hour. An unanticipated problem immediately showed up. It seems a 1.5 inch ABS pipe is 1.5 inch inside diameter, 1 and 7/8 outside and the flanges on the original ABS elbow are 2.25 inches in outside diameter. The floor "2x2's" are 1.25 inches. The manufacturer squeezed a 2.25 inch elbow into a 1.25 inch space by bending the thin lower plywood and aluminum sheeting! My rubber elbow is even larger - 2 and 3/8 inches. I spent considerable time digging into the top of floor plywood where the rubber flange had to go so it actually fit in without bending the pipe. Hopefully this will eliminate any more pipe cracks.
I am now working on the routine inside cupboard piping which has to be slightly different to accommodate the length losses due to the two cuts that took out the broken elbow. I'm using one rubber joint to make it a little easier to work with, better able to handle road bumps and make it possible to take apart. It also makes cleaning the sink traps considerably easier.
Will post a couple of photos when finished.